diff --git a/package/hiawatha/hiawatha.mk b/package/hiawatha/hiawatha.mk
index 14d3c9f1ee..25da98a43c 100644
--- a/package/hiawatha/hiawatha.mk
+++ b/package/hiawatha/hiawatha.mk
@@ -15,6 +15,7 @@ HIAWATHA_CPE_ID_VENDOR = hiawatha-webserver
 HIAWATHA_CONF_OPTS = \
 	-DINSTALL_MBEDTLS_HEADERS=OFF \
 	-DUSE_SYSTEM_MBEDTLS=OFF \
+	-DCMAKE_C_FLAGS="$(TARGET_CFLAGS) -std=c99" \
 	-DENABLE_TOOLKIT=OFF \
 	-DCONFIG_DIR=/etc/hiawatha \
 	-DLOG_DIR=/var/log \