diff --git a/common.h b/common.h
index 3ef4b75..5192fa6 100644
--- a/common.h
+++ b/common.h
@@ -36,6 +36,7 @@
 
 #include <iomanip>
 #include <iostream>
+#include <cstdlib>
 #include <cstring>
 #include <limits>
 #include <stdexcept>