diff --git a/include/mbedtls/threading.h b/include/mbedtls/threading.h
index 4cfaadd..0707152 100644
--- a/include/mbedtls/threading.h
+++ b/include/mbedtls/threading.h
@@ -103,9 +103,9 @@
 #if !defined(_WIN32) && (defined(__unix__) || \
     (defined(__APPLE__) && defined(__MACH__)))
 #include <unistd.h>
-#if !defined(_POSIX_VERSION)
+#if !defined(_POSIX_VERSION) || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS
 extern mbedtls_threading_mutex_t mbedtls_threading_gmtime_mutex;
-#endif /* !_POSIX_VERSION */
+#endif /* !_POSIX_VERSION || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS */
 #endif /* !_WIN32 && (__unix__ || (__APPLE__ && __MACH__)) */
 #endif /* MBEDTLS_HAVE_TIME_DATE */
 #endif /* MBEDTLS_THREADING_C */