diff --git a/library/platform_util.c b/library/platform_util.c
index c248cf5..8bd53c6 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -75,7 +75,7 @@
 }
 #endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */
 
-#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_ALT)
+#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
 #include <time.h>
 #if !defined(_WIN32) && (defined(unix) || \
     defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
@@ -94,8 +94,8 @@
 #endif /* !_WIN32 && (unix || __unix || __unix__ ||
         * (__APPLE__ && __MACH__)) */
 
-struct tm *mbedtls_platform_gmtime( const mbedtls_time_t *tt,
-                                    struct tm *tm_buf )
+struct tm *mbedtls_platform_gmtime_r( const mbedtls_time_t *tt,
+                                      struct tm *tm_buf )
 {
 #if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
     return( ( gmtime_s( tm_buf, tt ) == 0 ) ? tm_buf : NULL );
@@ -124,4 +124,4 @@
     return( ( lt == NULL ) ? NULL : tm_buf );
 #endif /* _WIN32 && !EFIX64 && !EFI32 */
 }
-#endif /* MBEDTLS_HAVE_TIME_DATE && MBEDTLS_PLATFORM_GMTIME_ALT */
+#endif /* MBEDTLS_HAVE_TIME_DATE && MBEDTLS_PLATFORM_GMTIME_R_ALT */
diff --git a/library/threading.c b/library/threading.c
index 1885efd..3abb17c 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -37,7 +37,7 @@
 
 #include "mbedtls/threading.h"
 
-#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_ALT)
+#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
 #if !defined(_WIN32) && (defined(unix) || \
     defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
     defined(__MACH__)))
@@ -54,7 +54,7 @@
 #endif /* !_POSIX_VERSION || 200112L > _POSIX_THREAD_SAFE_FUNCTIONS */
 #endif /* !_WIN32 && (unix || __unix || __unix__ ||
         * (__APPLE__ && __MACH__)) */
-#endif /* MBEDTLS_HAVE_TIME_DATE && !MBEDTLS_PLATFORM_GMTIME_ALT */
+#endif /* MBEDTLS_HAVE_TIME_DATE && !MBEDTLS_PLATFORM_GMTIME_R_ALT */
 
 #if defined(MBEDTLS_THREADING_PTHREAD)
 static void threading_mutex_init_pthread( mbedtls_threading_mutex_t *mutex )
diff --git a/library/x509.c b/library/x509.c
index c17697b..52b5b64 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -898,7 +898,7 @@
     int ret = 0;
 
     tt = mbedtls_time( NULL );
-    lt = mbedtls_platform_gmtime( &tt, &tm_buf );
+    lt = mbedtls_platform_gmtime_r( &tt, &tm_buf );
 
     if( lt == NULL )
         ret = -1;