diff --git a/features/mbedtls/inc/mbedtls/platform.h b/features/mbedtls/inc/mbedtls/platform.h
index 801a948bc5c..71688bdcf0f 100644
--- a/features/mbedtls/inc/mbedtls/platform.h
+++ b/features/mbedtls/inc/mbedtls/platform.h
@@ -257,6 +257,7 @@ int mbedtls_platform_set_snprintf( int (*snprintf_func)( char * s, size_t n,
  */
 #if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
 /* For Older Windows (inc. MSYS2), we provide our own fixed implementation */
+#include <stdarg.h>
 int mbedtls_platform_win32_vsnprintf( char *s, size_t n, const char *fmt, va_list arg );
 #endif