diff --git a/src/hammer.h b/src/hammer.h
index 79e3bd98e3d2c1b096b4ef122eef016dbe7509b7..0791769d729f83a059dcfa030a8b692636e30759 100644
--- a/src/hammer.h
+++ b/src/hammer.h
@@ -17,6 +17,7 @@
 
 #ifndef HAMMER_HAMMER__H
 #define HAMMER_HAMMER__H
+#include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
 #include "allocator.h"