diff --git a/dgl/src/TopLevelWidget.cpp b/dgl/src/TopLevelWidget.cpp
index aa3bede9..2c9f1c02 100644
--- a/dgl/src/TopLevelWidget.cpp
+++ b/dgl/src/TopLevelWidget.cpp
@@ -15,6 +15,7 @@
  */
 
 #include "TopLevelWidgetPrivateData.hpp"
+#include "../Window.hpp"
 
 START_NAMESPACE_DGL