diff --git a/library/debug.c b/library/debug.c
index 672e04537..2a559b54b 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -65,7 +65,16 @@ void mbedtls_debug_print_msg( const mbedtls_ssl_context *ssl, int level,
 
     va_start( argp, format );
 #if defined(_WIN32)
+#if defined(_TRUNCATE)
     ret = _vsnprintf_s( str, DEBUG_BUF_SIZE, _TRUNCATE, format, argp );
+#else
+    ret = _vsnprintf( str, DEBUG_BUF_SIZE, format, argp );
+    if( ret < 0 || (size_t) ret == DEBUG_BUF_SIZE )
+    {
+        str[DEBUG_BUF_SIZE-1] = '\0';
+        ret = -1;
+    }
+#endif
 #else
     ret = vsnprintf( str, DEBUG_BUF_SIZE, format, argp );
 #endif
diff --git a/library/platform.c b/library/platform.c
index 0606214b3..3161a4c00 100644
--- a/library/platform.c
+++ b/library/platform.c
@@ -75,7 +75,16 @@ int mbedtls_platform_win32_snprintf( char *s, size_t n, const char *fmt, ... )
         return( -1 );
 
     va_start( argp, fmt );
+#if defined(_TRUNCATE)
     ret = _vsnprintf_s( s, n, _TRUNCATE, fmt, argp );
+#else
+    ret = _vsnprintf( s, n, fmt, argp );
+    if( ret < 0 || (size_t) ret == n )
+    {
+        s[n-1] = '\0';
+        ret = -1;
+    }
+#endif
     va_end( argp );
 
     return( ret );