diff --git a/doomsday/client/include/ui/clientwindow.h b/doomsday/client/include/ui/clientwindow.h
index 5d66abfcf3..0b1234d268 100644
--- a/doomsday/client/include/ui/clientwindow.h
+++ b/doomsday/client/include/ui/clientwindow.h
@@ -161,7 +161,7 @@ class ClientWindow : public de::BaseWindow,
     void canvasGLResized(de::Canvas &);
 
     // Implements BaseWindow.
-    de::Vector2f windowContentSize();
+    de::Vector2f windowContentSize() const;
     void drawWindowContent();
     void preDraw();
     void postDraw();
diff --git a/doomsday/client/src/ui/clientwindow.cpp b/doomsday/client/src/ui/clientwindow.cpp
index 00ce8d46dc..4e45e05acd 100644
--- a/doomsday/client/src/ui/clientwindow.cpp
+++ b/doomsday/client/src/ui/clientwindow.cpp
@@ -683,9 +683,9 @@ ClientWindow::ClientWindow(String const &id)
     d->setupUI();
 }
 
-Vector2f ClientWindow::windowContentSize()
+Vector2f ClientWindow::windowContentSize() const
 {
-    return Vector2f(root().viewWidth().value(), root().viewHeight().value());
+    return Vector2f(d->root.viewWidth().value(), d->root.viewHeight().value());
 }
 
 ClientRootWidget &ClientWindow::root()
diff --git a/doomsday/libappfw/include/de/framework/basewindow.h b/doomsday/libappfw/include/de/framework/basewindow.h
index 8a3fd63b3c..47d1832d4e 100644
--- a/doomsday/libappfw/include/de/framework/basewindow.h
+++ b/doomsday/libappfw/include/de/framework/basewindow.h
@@ -65,7 +65,7 @@ class LIBAPPFW_PUBLIC BaseWindow : public PersistentCanvasWindow
     /**
      * Returns the logical size of the window contents (e.g., root widget).
      */
-    virtual Vector2f windowContentSize() = 0;
+    virtual Vector2f windowContentSize() const = 0;
 
     /**
      * Causes the contents of the window to be drawn. The contents are drawn immediately