diff --git a/Userland/Libraries/LibGUI/UndoStack.h b/Userland/Libraries/LibGUI/UndoStack.h
index 5c2b829219..3f720ebd01 100644
--- a/Userland/Libraries/LibGUI/UndoStack.h
+++ b/Userland/Libraries/LibGUI/UndoStack.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Function.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <LibGUI/Forward.h>