diff --git a/src/client/mac/handler/breakpad_nlist_64.h b/src/client/mac/handler/breakpad_nlist_64.h
index 1d2c639..e8e2e08 100644
--- a/src/client/mac/handler/breakpad_nlist_64.h
+++ b/src/client/mac/handler/breakpad_nlist_64.h
@@ -32,6 +32,7 @@
 // nlist function implemented to work on 64-bit.
 
 #ifndef CLIENT_MAC_HANDLER_BREAKPAD_NLIST_H__
+#define CLIENT_MAC_HANDLER_BREAKPAD_NLIST_H__
 
 #include <mach/machine.h>