diff --git a/tools/common/utils.h b/tools/common/utils.h
index 42c2753..b85e45c 100644
--- a/tools/common/utils.h
+++ b/tools/common/utils.h
@@ -1,5 +1,6 @@
 #pragma once
 #include <algorithm>
+#include <cctype>
 #include <cstdint>
 #include <cstring>
 #include <string>