diff --git a/include/mbedtls/threading.h b/include/mbedtls/threading.h
index c25daa5..4cfaadd 100644
--- a/include/mbedtls/threading.h
+++ b/include/mbedtls/threading.h
@@ -99,6 +99,15 @@
 #if defined(MBEDTLS_FS_IO)
 extern mbedtls_threading_mutex_t mbedtls_threading_readdir_mutex;
 #endif
+#if defined(MBEDTLS_HAVE_TIME_DATE)
+#if !defined(_WIN32) && (defined(__unix__) || \
+    (defined(__APPLE__) && defined(__MACH__)))
+#include <unistd.h>
+#if !defined(_POSIX_VERSION)
+extern mbedtls_threading_mutex_t mbedtls_threading_gmtime_mutex;
+#endif /* !_POSIX_VERSION */
+#endif /* !_WIN32 && (__unix__ || (__APPLE__ && __MACH__)) */
+#endif /* MBEDTLS_HAVE_TIME_DATE */
 #endif /* MBEDTLS_THREADING_C */
 
 #ifdef __cplusplus