diff --git a/tests/sub.c b/tests/sub.c
index 70f3749..69310d1 100644
--- a/tests/sub.c
+++ b/tests/sub.c
@@ -1,4 +1,5 @@
 #include "sub.h"
+#include <stdio.h>
 
 int sub(int a, int b)
 {