diff --git a/include/wx/graphics.h b/include/wx/graphics.h
index ef8501e4ed..8d6c126e7b 100644
--- a/include/wx/graphics.h
+++ b/include/wx/graphics.h
@@ -491,7 +491,7 @@ public:
 
 
     virtual void GetTextExtent( const wxString &text, wxDouble *width, wxDouble *height,
-        wxDouble *descent, wxDouble *externalLeading ) const  = 0;
+        wxDouble *descent = NULL, wxDouble *externalLeading = NULL ) const  = 0;
 
     virtual void GetPartialTextExtents(const wxString& text, wxArrayDouble& widths) const = 0;