diff --git a/include/wx/toplevel.h b/include/wx/toplevel.h
index 1fc0ef0466..5c446d89a7 100644
--- a/include/wx/toplevel.h
+++ b/include/wx/toplevel.h
@@ -325,6 +325,8 @@ protected:
         DoGetPosition(x, y);
     }
 
+    virtual wxSize DoGetBestClientSize() const override;
+
     // test whether this window makes part of the frame
     // (menubar, toolbar and statusbar are excluded from automatic layout)
     virtual bool IsOneOfBars(const wxWindow *WXUNUSED(win)) const
diff --git a/src/common/toplvcmn.cpp b/src/common/toplvcmn.cpp
index c7224e6962..c0da2a47c1 100644
--- a/src/common/toplvcmn.cpp
+++ b/src/common/toplvcmn.cpp
@@ -486,6 +486,18 @@ bool wxTopLevelWindowBase::Layout()
     return false;
 }
 
+wxSize wxTopLevelWindowBase::DoGetBestClientSize() const
+{
+    // The logic here parallels that of Layout() above.
+    if ( !UsesAutoLayout() )
+    {
+        if ( wxWindow* const child = GetUniqueChild() )
+            return child->GetBestSize();
+    }
+
+    return wxNonOwnedWindow::DoGetBestClientSize();
+}
+
 // The default implementation for the close window event.
 void wxTopLevelWindowBase::OnCloseWindow(wxCloseEvent& WXUNUSED(event))
 {