diff --git a/src/osx/cocoa/window.mm b/src/osx/cocoa/window.mm
index c59f374f32..a8ab324dd0 100644
--- a/src/osx/cocoa/window.mm
+++ b/src/osx/cocoa/window.mm
@@ -3311,7 +3311,7 @@ void wxWidgetCocoaImpl::SetBackgroundColour( const wxColour &col )
         wxWindow* peer = GetWXPeer();
         if ( peer->GetBackgroundStyle() != wxBG_STYLE_TRANSPARENT )
         {
-            wxTopLevelWindow* toplevel = wxDynamicCast(peer,wxTopLevelWindow);
+            wxNonOwnedWindow* toplevel = dynamic_cast<wxNonOwnedWindow*>(peer);
 
             if ( toplevel == nullptr || toplevel->GetShape().IsEmpty() )
                 [targetView setBackgroundColor:
diff --git a/src/osx/nonownedwnd_osx.cpp b/src/osx/nonownedwnd_osx.cpp
index c9781afe71..2781cbd70f 100644
--- a/src/osx/nonownedwnd_osx.cpp
+++ b/src/osx/nonownedwnd_osx.cpp
@@ -258,7 +258,9 @@ bool wxNonOwnedWindow::SetBackgroundColour(const wxColour& c )
     // only set the native background color if the toplevel window's
     // background is not supposed to be transparent, otherwise the
     // transparency is lost
-    if ( GetBackgroundStyle() != wxBG_STYLE_PAINT && GetBackgroundStyle() != wxBG_STYLE_TRANSPARENT)
+    // we cannot set the background color on a shaped toplevel window
+    // otherwise we loose the shape and end up with a rectangular background
+    if ( GetBackgroundStyle() != wxBG_STYLE_PAINT && GetBackgroundStyle() != wxBG_STYLE_TRANSPARENT && GetShape().IsEmpty() )
     {
         if ( m_nowpeer )
             return m_nowpeer->SetBackgroundColour(c);