diff --git a/include/mbedtls/threading.h b/include/mbedtls/threading.h
index 2e61b2e..11f6341 100644
--- a/include/mbedtls/threading.h
+++ b/include/mbedtls/threading.h
@@ -112,14 +112,18 @@
     defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
     defined(__MACH__)))
 #include <unistd.h>
-#if !defined(_POSIX_VERSION) || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS
+#if !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
+       ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
+         _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) )
 /*
  * The preprocessor conditions above are the same as in platform_util.c and
  * threading.c. Remember to update the code there when changing the conditions
  * here.
  */
 extern mbedtls_threading_mutex_t mbedtls_threading_gmtime_mutex;
-#endif /* !_POSIX_VERSION || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS */
+#endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
+             ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
+                _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) ) */
 #endif /* !_WIN32 && (unix || __unix || __unix__ ||
         * (__APPLE__ && __MACH__)) */
 #endif /* MBEDTLS_HAVE_TIME_DATE && !MBEDTLS_PLATFORM_GMTIME_R_ALT */