diff --git a/src/Gui/ActiveObjectList.h b/src/Gui/ActiveObjectList.h
index 636d271411..cd40323145 100644
--- a/src/Gui/ActiveObjectList.h
+++ b/src/Gui/ActiveObjectList.h
@@ -27,6 +27,7 @@
 #define GUI_ActiveObjectList_H
 
 #include <map>
+#include <string>
 #include <Gui/TreeItemMode.h>
 #include <FCGlobal.h>