diff --git a/package/conmon/conmon.mk b/package/conmon/conmon.mk
index 214cb460a5..1e57786686 100644
--- a/package/conmon/conmon.mk
+++ b/package/conmon/conmon.mk
@@ -25,7 +25,8 @@ define CONMON_CONFIGURE_CMDS
 endef
 
 define CONMON_BUILD_CMDS
-	$(TARGET_MAKE_ENV) $(MAKE) CC="$(TARGET_CC)" CFLAGS="$(TARGET_CFLAGS)" \
+	$(TARGET_MAKE_ENV) $(MAKE) CC="$(TARGET_CC)" \
+		CFLAGS="$(TARGET_CFLAGS) -std=c99" \
 		LDFLAGS="$(TARGET_LDFLAGS)" -C $(@D) bin/conmon
 endef