diff --git a/include/wx/mac/listbox.h b/include/wx/mac/listbox.h
index 0df5bd0366..77c0f27209 100644
--- a/include/wx/mac/listbox.h
+++ b/include/wx/mac/listbox.h
@@ -149,7 +149,7 @@ protected:
     int             MacGetSelections(wxArrayInt& aSelections) const ;
     bool            MacIsSelected( int n ) const ;
     void            MacScrollTo( int n ) ;
-    void            OnSize( const wxSizeEvent &size ) ;
+    void            OnSize( wxSizeEvent &size ) ;
     void            MacDoClick() ;
     void            MacDoDoubleClick() ;
 
diff --git a/src/mac/carbon/listbox.cpp b/src/mac/carbon/listbox.cpp
index 128f87af9e..4a623eb59b 100644
--- a/src/mac/carbon/listbox.cpp
+++ b/src/mac/carbon/listbox.cpp
@@ -823,7 +823,7 @@ void wxListBox::MacScrollTo( int n )
     // TODO implement scrolling
 }
 
-void wxListBox::OnSize( const wxSizeEvent &event)
+void wxListBox::OnSize( wxSizeEvent &event)
 {
     Point pt;
     
diff --git a/src/mac/listbox.cpp b/src/mac/listbox.cpp
index 128f87af9e..4a623eb59b 100644
--- a/src/mac/listbox.cpp
+++ b/src/mac/listbox.cpp
@@ -823,7 +823,7 @@ void wxListBox::MacScrollTo( int n )
     // TODO implement scrolling
 }
 
-void wxListBox::OnSize( const wxSizeEvent &event)
+void wxListBox::OnSize( wxSizeEvent &event)
 {
     Point pt;