diff --git a/googlemock/include/gmock/gmock-function-mocker.h b/googlemock/include/gmock/gmock-function-mocker.h
index 36bab78..e6913e5 100644
--- a/googlemock/include/gmock/gmock-function-mocker.h
+++ b/googlemock/include/gmock/gmock-function-mocker.h
@@ -62,6 +62,39 @@
   }
 };
 
+constexpr bool PrefixOf(const char* a, const char* b) {
+  return *a == 0 || (*a == *b && internal::PrefixOf(a + 1, b + 1));
+}
+
+template <int N, int M>
+constexpr bool StartsWith(const char (&prefix)[N], const char (&str)[M]) {
+  return N <= M && internal::PrefixOf(prefix, str);
+}
+
+template <int N, int M>
+constexpr bool EndsWith(const char (&suffix)[N], const char (&str)[M]) {
+  return N <= M && internal::PrefixOf(suffix, str + M - N);
+}
+
+template <int N, int M>
+constexpr bool Equals(const char (&a)[N], const char (&b)[M]) {
+  return N == M && internal::PrefixOf(a, b);
+}
+
+template <int N>
+constexpr bool ValidateSpec(const char (&spec)[N]) {
+  return internal::Equals("const", spec) ||
+         internal::Equals("override", spec) ||
+         internal::Equals("final", spec) ||
+         internal::Equals("noexcept", spec) ||
+         (internal::StartsWith("noexcept(", spec) &&
+          internal::EndsWith(")", spec)) ||
+         internal::Equals("ref(&)", spec) ||
+         internal::Equals("ref(&&)", spec) ||
+         (internal::StartsWith("Calltype(", spec) &&
+          internal::EndsWith(")", spec));
+}
+
 }  // namespace internal
 
 // The style guide prohibits "using" statements in a namespace scope
@@ -84,17 +117,18 @@
 #define GMOCK_INTERNAL_MOCK_METHOD_ARG_3(_Ret, _MethodName, _Args) \
   GMOCK_INTERNAL_MOCK_METHOD_ARG_4(_Ret, _MethodName, _Args, ())
 
-#define GMOCK_INTERNAL_MOCK_METHOD_ARG_4(_Ret, _MethodName, _Args, _Spec)     \
-  GMOCK_INTERNAL_ASSERT_PARENTHESIS(_Args);                                   \
-  GMOCK_INTERNAL_ASSERT_PARENTHESIS(_Spec);                                   \
-  GMOCK_INTERNAL_ASSERT_VALID_SIGNATURE(                                      \
-      GMOCK_PP_NARG0 _Args, GMOCK_INTERNAL_SIGNATURE(_Ret, _Args));           \
-  GMOCK_INTERNAL_ASSERT_VALID_SPEC(_Spec)                                     \
-  GMOCK_INTERNAL_MOCK_METHOD_IMPL(                                            \
-      GMOCK_PP_NARG0 _Args, _MethodName, GMOCK_INTERNAL_HAS_CONST(_Spec),     \
-      GMOCK_INTERNAL_HAS_OVERRIDE(_Spec), GMOCK_INTERNAL_HAS_FINAL(_Spec),    \
-      GMOCK_INTERNAL_GET_NOEXCEPT_SPEC(_Spec),                                \
-      GMOCK_INTERNAL_GET_CALLTYPE(_Spec), GMOCK_INTERNAL_GET_REF_SPEC(_Spec), \
+#define GMOCK_INTERNAL_MOCK_METHOD_ARG_4(_Ret, _MethodName, _Args, _Spec)  \
+  GMOCK_INTERNAL_ASSERT_PARENTHESIS(_Args);                                \
+  GMOCK_INTERNAL_ASSERT_PARENTHESIS(_Spec);                                \
+  GMOCK_INTERNAL_ASSERT_VALID_SIGNATURE(                                   \
+      GMOCK_PP_NARG0 _Args, GMOCK_INTERNAL_SIGNATURE(_Ret, _Args));        \
+  GMOCK_INTERNAL_ASSERT_VALID_SPEC(_Spec)                                  \
+  GMOCK_INTERNAL_MOCK_METHOD_IMPL(                                         \
+      GMOCK_PP_NARG0 _Args, _MethodName, GMOCK_INTERNAL_HAS_CONST(_Spec),  \
+      GMOCK_INTERNAL_HAS_OVERRIDE(_Spec), GMOCK_INTERNAL_HAS_FINAL(_Spec), \
+      GMOCK_INTERNAL_GET_NOEXCEPT_SPEC(_Spec),                             \
+      GMOCK_INTERNAL_GET_CALLTYPE_SPEC(_Spec),                             \
+      GMOCK_INTERNAL_GET_REF_SPEC(_Spec),                                  \
       (GMOCK_INTERNAL_SIGNATURE(_Ret, _Args)))
 
 #define GMOCK_INTERNAL_MOCK_METHOD_ARG_5(...) \
@@ -168,7 +202,7 @@
 
 #define GMOCK_INTERNAL_EXPAND(...) __VA_ARGS__
 
-// Five Valid modifiers.
+// Valid modifiers.
 #define GMOCK_INTERNAL_HAS_CONST(_Tuple) \
   GMOCK_PP_HAS_COMMA(GMOCK_PP_FOR_EACH(GMOCK_INTERNAL_DETECT_CONST, ~, _Tuple))
 
@@ -187,6 +221,14 @@
       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_NOEXCEPT(_i, _, _elem)), \
       _elem, )
 
+#define GMOCK_INTERNAL_GET_CALLTYPE_SPEC(_Tuple) \
+  GMOCK_PP_FOR_EACH(GMOCK_INTERNAL_CALLTYPE_SPEC_IF_CALLTYPE, ~, _Tuple)
+
+#define GMOCK_INTERNAL_CALLTYPE_SPEC_IF_CALLTYPE(_i, _, _elem)          \
+  GMOCK_PP_IF(                                                          \
+      GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_CALLTYPE(_i, _, _elem)), \
+      GMOCK_PP_CAT(GMOCK_INTERNAL_UNPACK_, _elem), )
+
 #define GMOCK_INTERNAL_GET_REF_SPEC(_Tuple) \
   GMOCK_PP_FOR_EACH(GMOCK_INTERNAL_REF_SPEC_IF_REF, ~, _Tuple)
 
@@ -194,19 +236,25 @@
   GMOCK_PP_IF(GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_REF(_i, _, _elem)), \
               GMOCK_PP_CAT(GMOCK_INTERNAL_UNPACK_, _elem), )
 
-#define GMOCK_INTERNAL_GET_CALLTYPE(_Tuple) \
-  GMOCK_PP_FOR_EACH(GMOCK_INTERNAL_GET_CALLTYPE_IMPL, ~, _Tuple)
-
-#define GMOCK_INTERNAL_ASSERT_VALID_SPEC_ELEMENT(_i, _, _elem)            \
-  static_assert(                                                          \
-      (GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_CONST(_i, _, _elem)) +    \
-       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_OVERRIDE(_i, _, _elem)) + \
-       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_FINAL(_i, _, _elem)) +    \
-       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_NOEXCEPT(_i, _, _elem)) + \
-       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_REF(_i, _, _elem)) +      \
-       GMOCK_INTERNAL_IS_CALLTYPE(_elem)) == 1,                           \
-      GMOCK_PP_STRINGIZE(                                                 \
+#ifdef GMOCK_INTERNAL_STRICT_SPEC_ASSERT
+#define GMOCK_INTERNAL_ASSERT_VALID_SPEC_ELEMENT(_i, _, _elem) \
+  static_assert(                                                     \
+      ::testing::internal::ValidateSpec(GMOCK_PP_STRINGIZE(_elem)),  \
+      "Token \'" GMOCK_PP_STRINGIZE(                                 \
+          _elem) "\' cannot be recognized as a valid specification " \
+                 "modifier. Is a ',' missing?");
+#else
+#define GMOCK_INTERNAL_ASSERT_VALID_SPEC_ELEMENT(_i, _, _elem)                 \
+  static_assert(                                                               \
+      (GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_CONST(_i, _, _elem)) +         \
+       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_OVERRIDE(_i, _, _elem)) +      \
+       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_FINAL(_i, _, _elem)) +         \
+       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_NOEXCEPT(_i, _, _elem)) +      \
+       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_REF(_i, _, _elem)) +           \
+       GMOCK_PP_HAS_COMMA(GMOCK_INTERNAL_DETECT_CALLTYPE(_i, _, _elem))) == 1, \
+      GMOCK_PP_STRINGIZE(                                                      \
           _elem) " cannot be recognized as a valid specification modifier.");
+#endif  // GMOCK_INTERNAL_STRICT_SPEC_ASSERT
 
 // Modifiers implementation.
 #define GMOCK_INTERNAL_DETECT_CONST(_i, _, _elem) \
@@ -236,26 +284,12 @@
 
 #define GMOCK_INTERNAL_UNPACK_ref(x) x
 
-#define GMOCK_INTERNAL_GET_CALLTYPE_IMPL(_i, _, _elem)           \
-  GMOCK_PP_IF(GMOCK_INTERNAL_IS_CALLTYPE(_elem),                 \
-              GMOCK_INTERNAL_GET_VALUE_CALLTYPE, GMOCK_PP_EMPTY) \
-  (_elem)
+#define GMOCK_INTERNAL_DETECT_CALLTYPE(_i, _, _elem) \
+  GMOCK_PP_CAT(GMOCK_INTERNAL_DETECT_CALLTYPE_I_, _elem)
 
-// TODO(iserna): GMOCK_INTERNAL_IS_CALLTYPE and
-// GMOCK_INTERNAL_GET_VALUE_CALLTYPE needed more expansions to work on windows
-// maybe they can be simplified somehow.
-#define GMOCK_INTERNAL_IS_CALLTYPE(_arg) \
-  GMOCK_INTERNAL_IS_CALLTYPE_I(          \
-      GMOCK_PP_CAT(GMOCK_INTERNAL_IS_CALLTYPE_HELPER_, _arg))
-#define GMOCK_INTERNAL_IS_CALLTYPE_I(_arg) GMOCK_PP_IS_ENCLOSED_PARENS(_arg)
+#define GMOCK_INTERNAL_DETECT_CALLTYPE_I_Calltype ,
 
-#define GMOCK_INTERNAL_GET_VALUE_CALLTYPE(_arg) \
-  GMOCK_INTERNAL_GET_VALUE_CALLTYPE_I(          \
-      GMOCK_PP_CAT(GMOCK_INTERNAL_IS_CALLTYPE_HELPER_, _arg))
-#define GMOCK_INTERNAL_GET_VALUE_CALLTYPE_I(_arg) \
-  GMOCK_PP_IDENTITY _arg
-
-#define GMOCK_INTERNAL_IS_CALLTYPE_HELPER_Calltype
+#define GMOCK_INTERNAL_UNPACK_Calltype(...) __VA_ARGS__
 
 // Note: The use of `identity_t` here allows _Ret to represent return types that
 // would normally need to be specified in a different way. For example, a method