diff --git a/src/client/linux/minidump_writer/linux_dumper_unittest_helper.cc b/src/client/linux/minidump_writer/linux_dumper_unittest_helper.cc
index 2dfe09b..3ad48e5 100644
--- a/src/client/linux/minidump_writer/linux_dumper_unittest_helper.cc
+++ b/src/client/linux/minidump_writer/linux_dumper_unittest_helper.cc
@@ -65,7 +65,7 @@
     perror("ERROR: parent notification failed");
     return NULL;
   }
-  volatile pid_t *thread_id_ptr asm(TID_PTR_REGISTER) = thread_id;
+  register volatile pid_t *thread_id_ptr asm(TID_PTR_REGISTER) = thread_id;
   while (true)
     asm volatile ("" : : "r" (thread_id_ptr));
   return NULL;