diff --git a/library/platform_util.c b/library/platform_util.c
index 35e29ae..25f5c57 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -95,7 +95,7 @@
     if (len > 0) {
 #if defined(MBEDTLS_PLATFORM_HAS_EXPLICIT_BZERO)
         explicit_bzero(buf, len);
-#elif(__STDC_LIB_EXT1__)
+#elif defined(__STDC_LIB_EXT1__)
         memset_s(buf, len, 0, len);
 #elif defined(_WIN32)
         SecureZeroMemory(buf, len);