diff --git a/src/plugins/projectexplorer/projectmacro.cpp b/src/plugins/projectexplorer/projectmacro.cpp
index e69e60421df..cdbd48772e7 100644
--- a/src/plugins/projectexplorer/projectmacro.cpp
+++ b/src/plugins/projectexplorer/projectmacro.cpp
@@ -26,6 +26,7 @@
 #include "projectmacro.h"
 
 #include <utils/algorithm.h>
+#include <cctype>
 
 namespace ProjectExplorer {