diff --git a/deps/c-ares/setup_once.h b/deps/c-ares/setup_once.h
index 37d797b36f9..0c7c811194c 100644
--- a/deps/c-ares/setup_once.h
+++ b/deps/c-ares/setup_once.h
@@ -33,6 +33,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdarg.h>
 #include <ctype.h>
 #include <errno.h>