diff --git a/CheckOther.cpp b/CheckOther.cpp
index 77375f35b..8b7917aa7 100644
--- a/CheckOther.cpp
+++ b/CheckOther.cpp
@@ -25,6 +25,7 @@
 #include <sstream>
 #include <stdlib.h>     // <- atoi
 #include <cstring>
+#include <cctype>
 //---------------------------------------------------------------------------