diff --git a/docs/symbol_files.md b/docs/symbol_files.md
index 9078201..237b656 100644
--- a/docs/symbol_files.md
+++ b/docs/symbol_files.md
@@ -100,12 +100,17 @@
 
 A `FUNC` record describes a source-language function. It has the form:
 
-> `FUNC` _address_ _size_ _parameter\_size_ _name_
+> `FUNC` _[m]_ _address_ _size_ _parameter\_size_ _name_
 
-For example: `FUNC c184 30 0 nsQueryInterfaceWithError::operator()(nsID const&,
+For example: `FUNC m c184 30 0 nsQueryInterfaceWithError::operator()(nsID const&,
 void**) const
 `
 
+The _m_ field is optional. If present it indicates that multiple symbols
+reference this function's instructions. (In which case, only one symbol name is
+mentioned within the breakpad file.) Multiple symbols referencing the same
+instructions may occur due to identical code folding by the linker.
+
 The _address_ and _size_ fields are hexadecimal numbers indicating the start
 address and length in bytes of the machine code instructions the function
 occupies. (Breakpad symbol files cannot accurately describe functions whose code
@@ -158,9 +163,9 @@
 to identify an assembly language entry point or region of memory. It has the
 form:
 
-> PUBLIC _address_ _parameter\_size_ _name_
+> PUBLIC _[m]_ _address_ _parameter\_size_ _name_
 
-For example: `PUBLIC 2160 0 Public2_1
+For example: `PUBLIC m 2160 0 Public2_1
 `
 
 The Breakpad processor essentially treats a `PUBLIC` record as defining a
@@ -168,6 +173,11 @@
 the next address mentioned. If a given address is covered by both a `PUBLIC`
 record and a `FUNC` record, the processor uses the `FUNC` data.
 
+The _m_ field is optional. If present it indicates that multiple symbols
+reference this function's instructions. (In which case, only one symbol name is
+mentioned within the breakpad file.) Multiple symbols referencing the same
+instructions may occur due to identical code folding by the linker.
+
 The _address_ field is a hexadecimal number indicating the symbol's address,
 relative to the module's load address.
 
diff --git a/src/common/windows/pdb_source_line_writer.cc b/src/common/windows/pdb_source_line_writer.cc
index dace886..19c6385 100644
--- a/src/common/windows/pdb_source_line_writer.cc
+++ b/src/common/windows/pdb_source_line_writer.cc
@@ -109,7 +109,53 @@
 
 using std::vector;
 
-typedef std::multimap<DWORD, CComPtr<IDiaSymbol>> SymbolMultimap;
+// The symbol (among possibly many) selected to represent an rva.
+struct SelectedSymbol {
+  SelectedSymbol(const CComPtr<IDiaSymbol>& symbol, bool is_public)
+      : symbol(symbol), is_public(is_public), is_multiple(false) {}
+
+  // The symbol to use for an rva.
+  CComPtr<IDiaSymbol> symbol;
+  // Whether this is a public or function symbol.
+  bool is_public;
+  // Whether the rva has multiple associated symbols. An rva will correspond to
+  // multiple symbols in the case of linker identical symbol folding.
+  bool is_multiple;
+};
+
+// Maps rva to the symbol to use for that address.
+typedef std::map<DWORD, SelectedSymbol> SymbolMap;
+
+// Record this in the map as the selected symbol for the rva if it satisfies the
+// necessary conditions.
+void MaybeRecordSymbol(DWORD rva,
+                       const CComPtr<IDiaSymbol> symbol,
+                       bool is_public,
+                       SymbolMap* map) {
+  SymbolMap::iterator loc = map->find(rva);
+  if (loc == map->end()) {
+    map->insert(std::make_pair(rva, SelectedSymbol(symbol, is_public)));
+    return;
+  }
+
+  // Prefer function symbols to public symbols.
+  if (is_public && !loc->second.is_public) {
+    return;
+  }
+
+  loc->second.is_multiple = true;
+
+  // Take the 'least' symbol by lexicographical order of the decorated name. We
+  // use the decorated rather than undecorated name because computing the latter
+  // is expensive.
+  BSTR current_name, new_name;
+  loc->second.symbol->get_name(&current_name);
+  symbol->get_name(&new_name);
+  if (wcscmp(new_name, current_name) < 0) {
+    loc->second.symbol = symbol;
+    loc->second.is_public = is_public;
+  }
+}
 
 // A helper class to scope a PLOADED_IMAGE.
 class AutoImage {
@@ -171,19 +217,10 @@
   return false;
 }
 
-// Computing undecorated names for all symbols is expensive, so we compare
-// decorated names.
-bool CompareSymbols(const SymbolMultimap::value_type& a,
-                    const SymbolMultimap::value_type& b) {
-  BSTR a_name, b_name;
-  a.second->get_name(&a_name);
-  b.second->get_name(&b_name);
-  return wcscmp(a_name, b_name) < 0;
-}
-
 }  // namespace
 
-PDBSourceLineWriter::PDBSourceLineWriter() : output_(NULL) {
+PDBSourceLineWriter::PDBSourceLineWriter(bool enable_multiple_field)
+    : enable_multiple_field_(enable_multiple_field), output_(NULL) {
 }
 
 PDBSourceLineWriter::~PDBSourceLineWriter() {
@@ -299,7 +336,8 @@
 }
 
 bool PDBSourceLineWriter::PrintFunction(IDiaSymbol *function,
-                                        IDiaSymbol *block) {
+                                        IDiaSymbol *block,
+                                        bool has_multiple_symbols) {
   // The function format is:
   // FUNC <address> <length> <param_stack_size> <function>
   DWORD rva;
@@ -335,9 +373,10 @@
   MapAddressRange(image_map_, AddressRange(rva, static_cast<DWORD>(length)),
                   &ranges);
   for (size_t i = 0; i < ranges.size(); ++i) {
-    fprintf(output_, "FUNC %lx %lx %x %ws\n",
-            ranges[i].rva, ranges[i].length, stack_param_size,
-            name.m_str);
+    const char* optional_multiple_field =
+      enable_multiple_field_ && has_multiple_symbols ? "m " : "";
+    fprintf(output_, "FUNC %s%lx %lx %x %ws\n", optional_multiple_field,
+            ranges[i].rva, ranges[i].length, stack_param_size, name.m_str);
   }
 
   CComPtr<IDiaEnumLineNumbers> lines;
@@ -415,7 +454,7 @@
   CComPtr<IDiaEnumSymbols> symbols = NULL;
 
   // Find all function symbols first.
-  SymbolMultimap rva_symbols;
+  SymbolMap rva_symbol;
   hr = global->findChildren(SymTagFunction, NULL, nsNone, &symbols);
 
   if (SUCCEEDED(hr)) {
@@ -423,10 +462,8 @@
 
     while (SUCCEEDED(symbols->Next(1, &symbol, &count)) && count == 1) {
       if (SUCCEEDED(symbol->get_relativeVirtualAddress(&rva))) {
-        // Place the symbols into a multimap indexed by rva, so we can choose
-        // the apropriate symbol name to use when multiple symbols share an
-        // address.
-        rva_symbols.insert(std::make_pair(rva, symbol));
+        // Potentially record this as the canonical symbol for this rva.
+        MaybeRecordSymbol(rva, symbol, false, &rva_symbol);
       } else {
         fprintf(stderr, "get_relativeVirtualAddress failed on the symbol\n");
         return false;
@@ -438,9 +475,8 @@
     symbols.Release();
   }
 
-  // Find all public symbols.  Store public symbols that are not also private
-  // symbols for later.
-  std::set<DWORD> public_only_rvas;
+  // Find all public symbols and record public symbols that are not also private
+  // symbols.
   hr = global->findChildren(SymTagPublicSymbol, NULL, nsNone, &symbols);
 
   if (SUCCEEDED(hr)) {
@@ -448,11 +484,8 @@
 
     while (SUCCEEDED(symbols->Next(1, &symbol, &count)) && count == 1) {
       if (SUCCEEDED(symbol->get_relativeVirtualAddress(&rva))) {
-        if (rva_symbols.find(rva) == rva_symbols.end()) {
-          // Keep symbols in rva order.
-          rva_symbols.insert(std::make_pair(rva, symbol));
-          public_only_rvas.insert(rva);
-        }
+        // Potentially record this as the canonical symbol for this rva.
+        MaybeRecordSymbol(rva, symbol, true, &rva_symbol);
       } else {
         fprintf(stderr, "get_relativeVirtualAddress failed on the symbol\n");
         return false;
@@ -464,29 +497,18 @@
     symbols.Release();
   }
 
-  // For each rva, dump one symbol at the address.
-  SymbolMultimap::iterator it = rva_symbols.begin();
-  while (it != rva_symbols.end()) {
-    std::pair<SymbolMultimap::iterator, SymbolMultimap::iterator> symbol_range =
-      rva_symbols.equal_range(it->first);
-    // Find the minimum symbol by name to make the output more consistent
-    // between runs on different releases of the same module, in the case of
-    // multiple symbols sharing an address.
-    SymbolMultimap::iterator least_symbol_iter =
-      std::min_element(symbol_range.first, symbol_range.second, CompareSymbols);
-    CComPtr<IDiaSymbol> symbol = least_symbol_iter->second;
+  // For each rva, dump the selected symbol at the address.
+  SymbolMap::iterator it;
+  for (it = rva_symbol.begin(); it != rva_symbol.end(); ++it) {
+    CComPtr<IDiaSymbol> symbol = it->second.symbol;
     // Only print public symbols if there is no function symbol for the address.
-    if (public_only_rvas.count(it->first) == 0) {
-      if (!PrintFunction(symbol, symbol))
+    if (!it->second.is_public) {
+      if (!PrintFunction(symbol, symbol, it->second.is_multiple))
         return false;
-      symbol.Release();
     } else {
-      if (!PrintCodePublicSymbol(symbol))
+      if (!PrintCodePublicSymbol(symbol, it->second.is_multiple))
         return false;
-      symbol.Release();
     }
-
-    it = symbol_range.second;
   }
 
   // When building with PGO, the compiler can split functions into
@@ -528,7 +550,7 @@
             SUCCEEDED(parent->get_relativeVirtualAddress(&func_rva)) &&
             SUCCEEDED(parent->get_length(&func_length))) {
           if (block_rva < func_rva || block_rva > (func_rva + func_length)) {
-            if (!PrintFunction(parent, block)) {
+            if (!PrintFunction(parent, block, false)) {
               return false;
             }
           }
@@ -845,7 +867,8 @@
   return false;
 }
 
-bool PDBSourceLineWriter::PrintCodePublicSymbol(IDiaSymbol *symbol) {
+bool PDBSourceLineWriter::PrintCodePublicSymbol(IDiaSymbol *symbol,
+                                                bool has_multiple_symbols) {
   BOOL is_code;
   if (FAILED(symbol->get_code(&is_code))) {
     return false;
@@ -868,8 +891,10 @@
   AddressRangeVector ranges;
   MapAddressRange(image_map_, AddressRange(rva, 1), &ranges);
   for (size_t i = 0; i < ranges.size(); ++i) {
-    fprintf(output_, "PUBLIC %lx %x %ws\n", ranges[i].rva,
-            stack_param_size > 0 ? stack_param_size : 0,
+    const char* optional_multiple_field =
+      enable_multiple_field_ && has_multiple_symbols ? "m " : "";
+    fprintf(output_, "PUBLIC %s%lx %x %ws\n", optional_multiple_field,
+            ranges[i].rva, stack_param_size > 0 ? stack_param_size : 0,
             name.m_str);
   }
 
diff --git a/src/common/windows/pdb_source_line_writer.h b/src/common/windows/pdb_source_line_writer.h
index e9e89bb..5a8bcbe 100644
--- a/src/common/windows/pdb_source_line_writer.h
+++ b/src/common/windows/pdb_source_line_writer.h
@@ -92,7 +92,9 @@
     ANY_FILE   // try PDB_FILE and then EXE_FILE
   };
 
-  explicit PDBSourceLineWriter();
+  // NB: |enable_multiple_field| is temporary while transitioning to enabling
+  // writing the multiple field permanently.
+  explicit PDBSourceLineWriter(bool enable_multiple_field = false);
   ~PDBSourceLineWriter();
 
   // Opens the given file.  For executable files, the corresponding pdb
@@ -138,11 +140,12 @@
   bool PrintLines(IDiaEnumLineNumbers *lines);
 
   // Outputs a function address and name, followed by its source line list.
-  // block can be the same object as function, or it can be a reference
-  // to a code block that is lexically part of this function, but
-  // resides at a separate address.
-  // Returns true on success.
-  bool PrintFunction(IDiaSymbol *function, IDiaSymbol *block);
+  // block can be the same object as function, or it can be a reference to a
+  // code block that is lexically part of this function, but resides at a
+  // separate address. If has_multiple_symbols is true, this function's
+  // instructions correspond to multiple symbols. Returns true on success.
+  bool PrintFunction(IDiaSymbol *function, IDiaSymbol *block,
+                     bool has_multiple_symbols);
 
   // Outputs all functions as described above.  Returns true on success.
   bool PrintFunctions();
@@ -167,8 +170,10 @@
 
   // Outputs a single public symbol address and name, if the symbol corresponds
   // to a code address.  Returns true on success.  If symbol is does not
-  // correspond to code, returns true without outputting anything.
-  bool PrintCodePublicSymbol(IDiaSymbol *symbol);
+  // correspond to code, returns true without outputting anything. If
+  // has_multiple_symbols is true, the symbol corresponds to a code address and
+  // the instructions correspond to multiple symbols.
+  bool PrintCodePublicSymbol(IDiaSymbol *symbol, bool has_multiple_symbols);
 
   // Outputs a line identifying the PDB file that is being dumped, along with
   // its uuid and age.
@@ -227,6 +232,10 @@
   // a failure, returns 0, which is also a valid number of bytes.
   static int GetFunctionStackParamSize(IDiaSymbol *function);
 
+  // True if the optional 'm' field on FUNC and PUBLIC for multiple symbols at
+  // the same address should be output.
+  bool enable_multiple_field_;
+
   // The filename of the PE file corresponding to the currently-open
   // pdb file.
   wstring code_file_;
diff --git a/src/google_breakpad/processor/basic_source_line_resolver.h b/src/google_breakpad/processor/basic_source_line_resolver.h
index 6bb6d86..91fb784 100644
--- a/src/google_breakpad/processor/basic_source_line_resolver.h
+++ b/src/google_breakpad/processor/basic_source_line_resolver.h
@@ -95,12 +95,14 @@
                         char **filename);  // out
 
   // Parses a |function_line| declaration.  Returns true on success.
-  // Format:  FUNC <address> <size> <stack_param_size> <name>.
+  // Format:  FUNC [<multiple>] <address> <size> <stack_param_size> <name>.
   // Notice, that this method modifies the input |function_line| which is why it
-  // can't be const.  On success, <address>, <size>, <stack_param_size>, and
-  // <name> are stored in |*address|, |*size|, |*stack_param_size|, and |*name|.
-  // No allocation is done, |*name| simply points inside |function_line|.
+  // can't be const.  On success, the presence of <multiple>, <address>, <size>,
+  // <stack_param_size>, and <name> are stored in |*is_multiple|, |*address|,
+  // |*size|, |*stack_param_size|, and |*name|.  No allocation is done, |*name|
+  // simply points inside |function_line|.
   static bool ParseFunction(char *function_line,     // in
+                            bool *is_multiple,       // out
                             uint64_t *address,       // out
                             uint64_t *size,          // out
                             long *stack_param_size,  // out
@@ -119,12 +121,14 @@
                         long *source_file);  // out
 
   // Parses a |public_line| declaration.  Returns true on success.
-  // Format:  PUBLIC <address> <stack_param_size> <name>
+  // Format:  PUBLIC [<multiple>] <address> <stack_param_size> <name>
   // Notice, that this method modifies the input |function_line| which is why
-  // it can't be const.  On success, <address>, <stack_param_size>, <name>
-  // are stored in |*address|, |*stack_param_size|, and |*name|.
-  // No allocation is done, |*name| simply points inside |public_line|.
+  // it can't be const.  On success, the presence of <multiple>, <address>,
+  // <stack_param_size>, <name> are stored in |*is_multiple|, |*address|,
+  // |*stack_param_size|, and |*name|.  No allocation is done, |*name| simply
+  // points inside |public_line|.
   static bool ParsePublicSymbol(char *public_line,       // in
+                                bool *is_multiple,       // out
                                 uint64_t *address,       // out
                                 long *stack_param_size,  // out
                                 char **name);            // out
diff --git a/src/processor/basic_source_line_resolver.cc b/src/processor/basic_source_line_resolver.cc
index aa66e15..c4aa949 100644
--- a/src/processor/basic_source_line_resolver.cc
+++ b/src/processor/basic_source_line_resolver.cc
@@ -62,6 +62,42 @@
 #define strtoull _strtoui64
 #endif
 
+namespace {
+
+// Utility function to tokenize given the presence of an optional initial
+// field. In this case, optional_field is the expected string for the optional
+// field, and max_tokens is the maximum number of tokens including the optional
+// field. Refer to the documentation for Tokenize for descriptions of the other
+// arguments.
+bool TokenizeWithOptionalField(char *line,
+                               const char *optional_field,
+                               const char *separators,
+                               int max_tokens,
+                               vector<char*> *tokens) {
+  // First tokenize assuming the optional field is not present.  If we then see
+  // the optional field, additionally tokenize the last token into two tokens.
+  if (!Tokenize(line, separators, max_tokens - 1, tokens)) {
+    return false;
+  }
+
+  if (strcmp(tokens->front(), optional_field) == 0) {
+    // The optional field is present. Split the last token in two to recover the
+    // field prior to the last.
+    vector<char*> last_tokens;
+    if (!Tokenize(tokens->back(), separators, 2, &last_tokens)) {
+      return false;
+    }
+    // Replace the previous last token with the two new tokens.
+    tokens->pop_back();
+    tokens->push_back(last_tokens[0]);
+    tokens->push_back(last_tokens[1]);
+  }
+
+  return true;
+}
+
+}  // namespace
+
 static const char *kWhitespace = " \r\n";
 static const int kMaxErrorsPrinted = 5;
 static const int kMaxErrorsBeforeBailing = 100;
@@ -323,13 +359,14 @@
 
 BasicSourceLineResolver::Function*
 BasicSourceLineResolver::Module::ParseFunction(char *function_line) {
+  bool is_multiple;
   uint64_t address;
   uint64_t size;
   long stack_param_size;
   char *name;
-  if (SymbolParseHelper::ParseFunction(function_line, &address, &size,
-                                       &stack_param_size, &name)) {
-    return new Function(name, address, size, stack_param_size);
+  if (SymbolParseHelper::ParseFunction(function_line, &is_multiple, &address,
+                                       &size, &stack_param_size, &name)) {
+    return new Function(name, address, size, stack_param_size, is_multiple);
   }
   return NULL;
 }
@@ -349,11 +386,12 @@
 }
 
 bool BasicSourceLineResolver::Module::ParsePublicSymbol(char *public_line) {
+  bool is_multiple;
   uint64_t address;
   long stack_param_size;
   char *name;
 
-  if (SymbolParseHelper::ParsePublicSymbol(public_line, &address,
+  if (SymbolParseHelper::ParsePublicSymbol(public_line, &is_multiple, &address,
                                            &stack_param_size, &name)) {
     // A few public symbols show up with an address of 0.  This has been seen
     // in the dumped output of ntdll.pdb for symbols such as _CIlog, _CIpow,
@@ -366,7 +404,8 @@
     }
 
     linked_ptr<PublicSymbol> symbol(new PublicSymbol(name, address,
-                                                     stack_param_size));
+                                                     stack_param_size,
+                                                     is_multiple));
     return public_symbols_.Store(address, symbol);
   }
   return false;
@@ -491,36 +530,39 @@
 }
 
 // static
-bool SymbolParseHelper::ParseFunction(char *function_line, uint64_t *address,
-                                      uint64_t *size, long *stack_param_size,
-                                      char **name) {
-  // FUNC <address> <size> <stack_param_size> <name>
+bool SymbolParseHelper::ParseFunction(char *function_line, bool *is_multiple,
+                                      uint64_t *address, uint64_t *size,
+                                      long *stack_param_size, char **name) {
+  // FUNC [<multiple>] <address> <size> <stack_param_size> <name>
   assert(strncmp(function_line, "FUNC ", 5) == 0);
   function_line += 5;  // skip prefix
 
   vector<char*> tokens;
-  if (!Tokenize(function_line, kWhitespace, 4, &tokens)) {
+  if (!TokenizeWithOptionalField(function_line, "m", kWhitespace, 5, &tokens)) {
     return false;
   }
 
+  *is_multiple = strcmp(tokens[0], "m") == 0;
+  int next_token = *is_multiple ? 1 : 0;
+
   char *after_number;
-  *address = strtoull(tokens[0], &after_number, 16);
+  *address = strtoull(tokens[next_token++], &after_number, 16);
   if (!IsValidAfterNumber(after_number) ||
       *address == std::numeric_limits<unsigned long long>::max()) {
     return false;
   }
-  *size = strtoull(tokens[1], &after_number, 16);
+  *size = strtoull(tokens[next_token++], &after_number, 16);
   if (!IsValidAfterNumber(after_number) ||
       *size == std::numeric_limits<unsigned long long>::max()) {
     return false;
   }
-  *stack_param_size = strtol(tokens[2], &after_number, 16);
+  *stack_param_size = strtol(tokens[next_token++], &after_number, 16);
   if (!IsValidAfterNumber(after_number) ||
       *stack_param_size == std::numeric_limits<long>::max() ||
       *stack_param_size < 0) {
     return false;
   }
-  *name = tokens[3];
+  *name = tokens[next_token++];
 
   return true;
 }
@@ -571,32 +613,35 @@
 }
 
 // static
-bool SymbolParseHelper::ParsePublicSymbol(char *public_line,
+bool SymbolParseHelper::ParsePublicSymbol(char *public_line, bool *is_multiple,
                                           uint64_t *address,
                                           long *stack_param_size,
                                           char **name) {
-  // PUBLIC <address> <stack_param_size> <name>
+  // PUBLIC [<multiple>] <address> <stack_param_size> <name>
   assert(strncmp(public_line, "PUBLIC ", 7) == 0);
   public_line += 7;  // skip prefix
 
   vector<char*> tokens;
-  if (!Tokenize(public_line, kWhitespace, 3, &tokens)) {
+  if (!TokenizeWithOptionalField(public_line, "m", kWhitespace, 4, &tokens)) {
     return false;
   }
 
+  *is_multiple = strcmp(tokens[0], "m") == 0;
+  int next_token = *is_multiple ? 1 : 0;
+
   char *after_number;
-  *address = strtoull(tokens[0], &after_number, 16);
+  *address = strtoull(tokens[next_token++], &after_number, 16);
   if (!IsValidAfterNumber(after_number) ||
       *address == std::numeric_limits<unsigned long long>::max()) {
     return false;
   }
-  *stack_param_size = strtol(tokens[1], &after_number, 16);
+  *stack_param_size = strtol(tokens[next_token++], &after_number, 16);
   if (!IsValidAfterNumber(after_number) ||
       *stack_param_size == std::numeric_limits<long>::max() ||
       *stack_param_size < 0) {
     return false;
   }
-  *name = tokens[2];
+  *name = tokens[next_token++];
 
   return true;
 }
diff --git a/src/processor/basic_source_line_resolver_types.h b/src/processor/basic_source_line_resolver_types.h
index a022bc0..89eb57e 100644
--- a/src/processor/basic_source_line_resolver_types.h
+++ b/src/processor/basic_source_line_resolver_types.h
@@ -60,11 +60,13 @@
   Function(const string &function_name,
            MemAddr function_address,
            MemAddr code_size,
-           int set_parameter_size) : Base(function_name,
-                                          function_address,
-                                          code_size,
-                                          set_parameter_size),
-                                     lines() { }
+           int set_parameter_size,
+           bool is_mutiple) : Base(function_name,
+                                   function_address,
+                                   code_size,
+                                   set_parameter_size,
+                                   is_mutiple),
+                              lines() { }
   RangeMap< MemAddr, linked_ptr<Line> > lines;
  private:
   typedef SourceLineResolverBase::Function Base;
diff --git a/src/processor/basic_source_line_resolver_unittest.cc b/src/processor/basic_source_line_resolver_unittest.cc
index 9fab8ca..90c3417 100644
--- a/src/processor/basic_source_line_resolver_unittest.cc
+++ b/src/processor/basic_source_line_resolver_unittest.cc
@@ -455,16 +455,19 @@
 }
 
 // Test parsing of valid FUNC lines.  The format is:
-// FUNC <address> <size> <stack_param_size> <name>
+// FUNC [<multiple>] <address> <size> <stack_param_size> <name>
 TEST(SymbolParseHelper, ParseFunctionValid) {
+  bool multiple;
   uint64_t address;
   uint64_t size;
   long stack_param_size;
   char *name;
 
   char kTestLine[] = "FUNC 1 2 3 function name";
-  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine, &address, &size,
-                                               &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine, &multiple, &address,
+                                               &size, &stack_param_size,
+                                               &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(1ULL, address);
   EXPECT_EQ(2ULL, size);
   EXPECT_EQ(3, stack_param_size);
@@ -472,25 +475,41 @@
 
   // Test hex address, size, and param size.
   char kTestLine1[] = "FUNC a1 a2 a3 function name";
-  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine1, &address, &size,
-                                               &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine1, &multiple, &address,
+                                               &size, &stack_param_size,
+                                               &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(0xa1ULL, address);
   EXPECT_EQ(0xa2ULL, size);
   EXPECT_EQ(0xa3, stack_param_size);
   EXPECT_EQ("function name", string(name));
 
   char kTestLine2[] = "FUNC 0 0 0 function name";
-  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine2, &address, &size,
-                                               &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine2, &multiple, &address,
+                                               &size, &stack_param_size,
+                                               &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(0ULL, address);
   EXPECT_EQ(0ULL, size);
   EXPECT_EQ(0, stack_param_size);
   EXPECT_EQ("function name", string(name));
+
+  // Test optional multiple field.
+  char kTestLine3[] = "FUNC m a1 a2 a3 function name";
+  ASSERT_TRUE(SymbolParseHelper::ParseFunction(kTestLine3, &multiple, &address,
+                                               &size, &stack_param_size,
+                                               &name));
+  EXPECT_TRUE(multiple);
+  EXPECT_EQ(0xa1ULL, address);
+  EXPECT_EQ(0xa2ULL, size);
+  EXPECT_EQ(0xa3, stack_param_size);
+  EXPECT_EQ("function name", string(name));
 }
 
 // Test parsing of invalid FUNC lines.  The format is:
-// FUNC <address> <size> <stack_param_size> <name>
+// FUNC [<multiple>] <address> <size> <stack_param_size> <name>
 TEST(SymbolParseHelper, ParseFunctionInvalid) {
+  bool multiple;
   uint64_t address;
   uint64_t size;
   long stack_param_size;
@@ -498,36 +517,49 @@
 
   // Test missing function name.
   char kTestLine[] = "FUNC 1 2 3 ";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test bad address.
   char kTestLine1[] = "FUNC 1z 2 3 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine1, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine1, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test large address.
   char kTestLine2[] = "FUNC 123123123123123123123123123 2 3 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine2, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine2, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test bad size.
   char kTestLine3[] = "FUNC 1 z2 3 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine3, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine3, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test large size.
   char kTestLine4[] = "FUNC 1 231231231231231231231231232 3 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine4, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine4, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test bad param size.
   char kTestLine5[] = "FUNC 1 2 3z function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine5, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine5, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Test large param size.
   char kTestLine6[] = "FUNC 1 2 312312312312312312312312323 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine6, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine6, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
   // Negative param size.
   char kTestLine7[] = "FUNC 1 2 -5 function name";
-  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine7, &address, &size,
-                                                &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine7, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
+  // Test invalid optional field.
+  char kTestLine8[] = "FUNC x 1 2 5 function name";
+  ASSERT_FALSE(SymbolParseHelper::ParseFunction(kTestLine8, &multiple, &address,
+                                                &size, &stack_param_size,
+                                                &name));
 }
 
 // Test parsing of valid lines.  The format is:
@@ -612,67 +644,96 @@
 }
 
 // Test parsing of valid PUBLIC lines.  The format is:
-// PUBLIC <address> <stack_param_size> <name>
+// PUBLIC [<multiple>] <address> <stack_param_size> <name>
 TEST(SymbolParseHelper, ParsePublicSymbolValid) {
+  bool multiple;
   uint64_t address;
   long stack_param_size;
   char *name;
 
   char kTestLine[] = "PUBLIC 1 2 3";
-  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine, &address,
-                                                   &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine, &multiple,
+                                                   &address, &stack_param_size,
+                                                   &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(1ULL, address);
   EXPECT_EQ(2, stack_param_size);
   EXPECT_EQ("3", string(name));
 
   // Test hex size and address.
   char kTestLine1[] = "PUBLIC a1 a2 function name";
-  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine1, &address,
-                                                   &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine1, &multiple,
+                                                   &address, &stack_param_size,
+                                                   &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(0xa1ULL, address);
   EXPECT_EQ(0xa2, stack_param_size);
   EXPECT_EQ("function name", string(name));
 
   // Test 0 is a valid address.
   char kTestLine2[] = "PUBLIC 0 a2 function name";
-  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine2, &address,
-                                                   &stack_param_size, &name));
+  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine2, &multiple,
+                                                   &address, &stack_param_size,
+                                                   &name));
+  EXPECT_FALSE(multiple);
   EXPECT_EQ(0ULL, address);
   EXPECT_EQ(0xa2, stack_param_size);
   EXPECT_EQ("function name", string(name));
+
+  // Test optional multiple field.
+  char kTestLine3[] = "PUBLIC m a1 a2 function name";
+  ASSERT_TRUE(SymbolParseHelper::ParsePublicSymbol(kTestLine3, &multiple,
+                                                   &address, &stack_param_size,
+                                                   &name));
+  EXPECT_TRUE(multiple);
+  EXPECT_EQ(0xa1ULL, address);
+  EXPECT_EQ(0xa2, stack_param_size);
+  EXPECT_EQ("function name", string(name));
 }
 
 // Test parsing of invalid PUBLIC lines.  The format is:
-// PUBLIC <address> <stack_param_size> <name>
+// PUBLIC [<multiple>] <address> <stack_param_size> <name>
 TEST(SymbolParseHelper, ParsePublicSymbolInvalid) {
+  bool multiple;
   uint64_t address;
   long stack_param_size;
   char *name;
 
   // Test missing source function name.
   char kTestLine[] = "PUBLIC 1 2 ";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
   // Test bad address.
   char kTestLine1[] = "PUBLIC 1z 2 3";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine1, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine1, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
   // Test large address.
   char kTestLine2[] = "PUBLIC 123123123123123123123123 2 3";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine2, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine2, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
   // Test bad param stack size.
   char kTestLine3[] = "PUBLIC 1 z2 3";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine3, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine3, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
   // Test large param stack size.
   char kTestLine4[] = "PUBLIC 1 123123123123123123123123123 3";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine4, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine4, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
   // Test negative param stack size.
   char kTestLine5[] = "PUBLIC 1 -5 3";
-  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine5, &address,
-                                                    &stack_param_size, &name));
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine5, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
+  // Test invalid optional field.
+  char kTestLine6[] = "PUBLIC x 1 5 3";
+  ASSERT_FALSE(SymbolParseHelper::ParsePublicSymbol(kTestLine6, &multiple,
+                                                    &address, &stack_param_size,
+                                                    &name));
 }
 
 }  // namespace
diff --git a/src/processor/source_line_resolver_base_types.h b/src/processor/source_line_resolver_base_types.h
index 4a9dfb3..ca744e0 100644
--- a/src/processor/source_line_resolver_base_types.h
+++ b/src/processor/source_line_resolver_base_types.h
@@ -85,9 +85,10 @@
   Function(const string &function_name,
            MemAddr function_address,
            MemAddr code_size,
-           int set_parameter_size)
+           int set_parameter_size,
+           bool is_multiple)
       : name(function_name), address(function_address), size(code_size),
-        parameter_size(set_parameter_size) { }
+        parameter_size(set_parameter_size), is_multiple(is_multiple) { }
 
   string name;
   MemAddr address;
@@ -95,16 +96,21 @@
 
   // The size of parameters passed to this function on the stack.
   int32_t parameter_size;
+
+  // If the function's instructions correspond to multiple symbols.
+  bool is_multiple;
 };
 
 struct SourceLineResolverBase::PublicSymbol {
   PublicSymbol() { }
   PublicSymbol(const string& set_name,
                MemAddr set_address,
-               int set_parameter_size)
+               int set_parameter_size,
+               bool is_multiple)
       : name(set_name),
         address(set_address),
-        parameter_size(set_parameter_size) {}
+        parameter_size(set_parameter_size),
+        is_multiple(is_multiple) {}
 
   string name;
   MemAddr address;
@@ -113,6 +119,9 @@
   // is set to the size of the parameters passed to the funciton on the
   // stack, if known.
   int32_t parameter_size;
+
+  // If the function's instructions correspond to multiple symbols.
+  bool is_multiple;
 };
 
 class SourceLineResolverBase::Module {
diff --git a/src/tools/windows/binaries/dump_syms.exe b/src/tools/windows/binaries/dump_syms.exe
index ca4676f..f27f3ec 100644
--- a/src/tools/windows/binaries/dump_syms.exe
+++ b/src/tools/windows/binaries/dump_syms.exe
Binary files differ
diff --git a/src/tools/windows/binaries/symupload.exe b/src/tools/windows/binaries/symupload.exe
index ba319b2..cdfee74 100644
--- a/src/tools/windows/binaries/symupload.exe
+++ b/src/tools/windows/binaries/symupload.exe
Binary files differ
diff --git a/src/tools/windows/dump_syms/dump_syms.cc b/src/tools/windows/dump_syms/dump_syms.cc
index 3e8827b..dcbe39a 100644
--- a/src/tools/windows/dump_syms/dump_syms.cc
+++ b/src/tools/windows/dump_syms/dump_syms.cc
@@ -31,6 +31,7 @@
 // a text-based format that we can use from the minidump processor.
 
 #include <stdio.h>
+#include <wchar.h>
 
 #include <string>
 
@@ -41,12 +42,22 @@
 
 int wmain(int argc, wchar_t **argv) {
   if (argc < 2) {
-    fprintf(stderr, "Usage: %ws <file.[pdb|exe|dll]>\n", argv[0]);
+    fprintf(stderr,
+            "Usage: %ws [--enable_multiple_field] <file.[pdb|exe|dll]>\n",
+            argv[0]);
     return 1;
   }
 
-  PDBSourceLineWriter writer;
-  if (!writer.Open(wstring(argv[1]), PDBSourceLineWriter::ANY_FILE)) {
+  // This is a temporary option to enable writing the optional 'm' field on FUNC
+  // and PUBLIC, denoting multiple symbols for the address. This option will be
+  // removed, with the behavior enabled by default, after all symbol file
+  // readers have had a chance to update.
+  bool enable_multiple_field =
+    (argc >= 3 && wcscmp(L"--enable_multiple_field", argv[1]) == 0);
+
+  PDBSourceLineWriter writer(enable_multiple_field);
+  if (!writer.Open(wstring(argv[enable_multiple_field ? 2 : 1]),
+                   PDBSourceLineWriter::ANY_FILE)) {
     fprintf(stderr, "Open failed\n");
     return 1;
   }
diff --git a/src/tools/windows/dump_syms/testdata/dump_syms_regtest64.sym b/src/tools/windows/dump_syms/testdata/dump_syms_regtest64.sym
index a43d3ae..3981524 100644
--- a/src/tools/windows/dump_syms/testdata/dump_syms_regtest64.sym
+++ b/src/tools/windows/dump_syms/testdata/dump_syms_regtest64.sym
@@ -1262,7 +1262,7 @@
 332a 5 107 69
 332f 7 108 69
 3336 a 109 69
-FUNC 3340 1 0 _NLG_Dispatch
+FUNC 3340 1 0 _NLG_Dispatch2
 3340 0 113 69
 3340 10 114 69
 FUNC 3350 1 0 _NLG_Return2