diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index 422180806a..34b19d732b 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -127,13 +127,13 @@ double modulo(double x, double y) {
 }
 
 
-static Mutex* math_function_mutex = OS::CreateMutex();
+static LazyMutex math_function_mutex = LAZY_MUTEX_INITIALIZER;
 
 #define UNARY_MATH_FUNCTION(name, generator)             \
 static UnaryMathFunction fast_##name##_function = NULL;  \
 double fast_##name(double x) {                           \
   if (fast_##name##_function == NULL) {                  \
-    ScopedLock lock(math_function_mutex);                \
+    ScopedLock lock(math_function_mutex.Pointer());      \
     UnaryMathFunction temp = generator;                  \
     MemoryBarrier();                                     \
     fast_##name##_function = temp;                       \
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index 2a25f044ef..16a5b0bc8a 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -208,13 +208,13 @@ double modulo(double x, double y) {
 #endif  // _WIN64
 
 
-static Mutex* math_function_mutex = OS::CreateMutex();
+static LazyMutex math_function_mutex = LAZY_MUTEX_INITIALIZER;
 
 #define UNARY_MATH_FUNCTION(name, generator)             \
 static UnaryMathFunction fast_##name##_function = NULL;  \
 double fast_##name(double x) {                           \
   if (fast_##name##_function == NULL) {                  \
-    ScopedLock lock(math_function_mutex);                \
+    ScopedLock lock(math_function_mutex.Pointer());      \
     UnaryMathFunction temp = generator;                  \
     MemoryBarrier();                                     \
     fast_##name##_function = temp;                       \