diff --git a/src/plugins/todo/cpptodoitemsscanner.cpp b/src/plugins/todo/cpptodoitemsscanner.cpp
index 8ee65353d10..c6062225186 100644
--- a/src/plugins/todo/cpptodoitemsscanner.cpp
+++ b/src/plugins/todo/cpptodoitemsscanner.cpp
@@ -33,6 +33,8 @@
 #include <projectexplorer/project.h>
 #include <cplusplus/TranslationUnit.h>
 
+#include <cctype>
+
 namespace Todo {
 namespace Internal {