diff --git a/FileIO/FEFLOWInterface.cpp b/FileIO/FEFLOWInterface.cpp
index 7092e237b6d7986e3344f5af57e74d572834ebb1..c760aefe248022e28ddd66be7020f0beafde36ca 100644
--- a/FileIO/FEFLOWInterface.cpp
+++ b/FileIO/FEFLOWInterface.cpp
@@ -8,6 +8,8 @@
 
 #include "FEFLOWInterface.h"
 
+#include <cctype>
+
 #include "logog/include/logog.hpp"
 #include <QtXml>