diff --git a/aos/util/file_test.cc b/aos/util/file_test.cc
index 6851302..7c93fb3 100644
--- a/aos/util/file_test.cc
+++ b/aos/util/file_test.cc
@@ -1,7 +1,6 @@
 #include "aos/util/file.h"
 
-#include <stdlib.h>
-
+#include <cstdlib>
 #include <string>
 
 #include "gtest/gtest.h"