diff --git a/src/osx/carbon/mdi.cpp b/src/osx/carbon/mdi.cpp
index 762f275734..216c16887e 100644
--- a/src/osx/carbon/mdi.cpp
+++ b/src/osx/carbon/mdi.cpp
@@ -360,7 +360,7 @@ void wxMDIChildFrame::MacActivate(long timestamp, bool activating)
 {
     wxLogTrace(TRACE_MDI, wxT("MDI child=%p  MacActivate(0x%08lx,%s)"),this, timestamp, activating ? wxT("ACTIV") : wxT("deact"));
 
-    wxMDIParentFrame *mdiparent = wxDynamicCast(m_parent, wxMDIParentFrame);
+    wxMDIParentFrame *mdiparent = m_mdiParent;
     wxASSERT(mdiparent);
 
     if (activating)