diff --git a/include/wx/gtk/glcanvas.h b/include/wx/gtk/glcanvas.h
index f4c812ffa8..30a548f8fa 100644
--- a/include/wx/gtk/glcanvas.h
+++ b/include/wx/gtk/glcanvas.h
@@ -116,14 +116,14 @@ public:
         long style = 0, const wxString& name = wxGLCanvasName,
         int *attribList = (int*) NULL,
         const wxPalette& palette = wxNullPalette );
-   wxGLCanvas( wxWindow *parent, const wxGLContext *shared = (wxGLContext *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLContext *shared,
         wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
         long style = 0, const wxString& name = wxGLCanvasName,
         int *attribList = (int*) NULL,
         const wxPalette& palette = wxNullPalette );
-   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared = (wxGLCanvas *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared,
         wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
diff --git a/include/wx/gtk1/glcanvas.h b/include/wx/gtk1/glcanvas.h
index f4c812ffa8..30a548f8fa 100644
--- a/include/wx/gtk1/glcanvas.h
+++ b/include/wx/gtk1/glcanvas.h
@@ -116,14 +116,14 @@ public:
         long style = 0, const wxString& name = wxGLCanvasName,
         int *attribList = (int*) NULL,
         const wxPalette& palette = wxNullPalette );
-   wxGLCanvas( wxWindow *parent, const wxGLContext *shared = (wxGLContext *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLContext *shared,
         wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
         long style = 0, const wxString& name = wxGLCanvasName,
         int *attribList = (int*) NULL,
         const wxPalette& palette = wxNullPalette );
-   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared = (wxGLCanvas *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared,
         wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
diff --git a/include/wx/mac/carbon/glcanvas.h b/include/wx/mac/carbon/glcanvas.h
index 465774cba4..2adfbf4d6f 100644
--- a/include/wx/mac/carbon/glcanvas.h
+++ b/include/wx/mac/carbon/glcanvas.h
@@ -89,12 +89,12 @@ class WXDLLEXPORT wxGLCanvas: public wxWindow
    wxGLCanvas(wxWindow *parent, wxWindowID id = -1, const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize, long style = 0,
         const wxString& name = wxT("GLCanvas") , int *attribList = 0, const wxPalette& palette = wxNullPalette);
-   wxGLCanvas( wxWindow *parent, const wxGLContext *shared = (wxGLContext *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLContext *shared,
         wxWindowID id = -1, const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize, long style = 0, const wxString& name = wxT("GLCanvas"), 
           int *attribList = (int*) NULL, const wxPalette& palette = wxNullPalette );
 
-   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared = (wxGLCanvas *)NULL, wxWindowID id = -1,
+   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared, wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxDefaultSize, long style = 0, 
         const wxString& name = wxT("GLCanvas"), int *attribList = 0, const wxPalette& palette = wxNullPalette );
 
diff --git a/include/wx/mac/classic/glcanvas.h b/include/wx/mac/classic/glcanvas.h
index f3f9635aca..558ad976e9 100644
--- a/include/wx/mac/classic/glcanvas.h
+++ b/include/wx/mac/classic/glcanvas.h
@@ -89,12 +89,12 @@ class WXDLLEXPORT wxGLCanvas: public wxWindow
    wxGLCanvas(wxWindow *parent, wxWindowID id = -1, const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize, long style = 0,
         const wxString& name = wxT("GLCanvas") , int *attribList = 0, const wxPalette& palette = wxNullPalette);
-   wxGLCanvas( wxWindow *parent, const wxGLContext *shared = (wxGLContext *)NULL,
+   wxGLCanvas( wxWindow *parent, const wxGLContext *shared,
         wxWindowID id = -1, const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize, long style = 0, const wxString& name = wxT("GLCanvas"), 
           int *attribList = (int*) NULL, const wxPalette& palette = wxNullPalette );
 
-   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared = (wxGLCanvas *)NULL, wxWindowID id = -1,
+   wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared, wxWindowID id = -1,
         const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxDefaultSize, long style = 0, 
         const wxString& name = wxT("GLCanvas"), int *attribList = 0, const wxPalette& palette = wxNullPalette );
 
diff --git a/include/wx/msw/glcanvas.h b/include/wx/msw/glcanvas.h
index 1cec4332fe..825c19dfc3 100644
--- a/include/wx/msw/glcanvas.h
+++ b/include/wx/msw/glcanvas.h
@@ -96,7 +96,7 @@ public:
         const wxPalette& palette = wxNullPalette);
 
     wxGLCanvas(wxWindow *parent,
-        const wxGLContext *shared = (wxGLContext *) NULL,
+        const wxGLContext *shared,
         wxWindowID id = wxID_ANY,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
@@ -106,7 +106,7 @@ public:
         const wxPalette& palette = wxNullPalette);
 
     wxGLCanvas(wxWindow *parent,
-        const wxGLCanvas *shared = (wxGLCanvas *)NULL,
+        const wxGLCanvas *shared,
         wxWindowID id = wxID_ANY,
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,
diff --git a/include/wx/x11/glcanvas.h b/include/wx/x11/glcanvas.h
index 575faeaf99..d5759175e1 100644
--- a/include/wx/x11/glcanvas.h
+++ b/include/wx/x11/glcanvas.h
@@ -103,14 +103,14 @@ public:
         long style = 0, const wxString& name = wxT("GLCanvas"), 
         int *attribList = (int*) NULL, 
         const wxPalette& palette = wxNullPalette );
-    wxGLCanvas( wxWindow *parent, const wxGLContext *shared = (wxGLContext *)NULL,
+    wxGLCanvas( wxWindow *parent, const wxGLContext *shared,
         wxWindowID id = -1, 
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize, 
         long style = 0, const wxString& name = wxT("GLCanvas"), 
         int *attribList = (int*) NULL, 
         const wxPalette& palette = wxNullPalette );
-    wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared = (wxGLCanvas *)NULL,
+    wxGLCanvas( wxWindow *parent, const wxGLCanvas *shared,
         wxWindowID id = -1, 
         const wxPoint& pos = wxDefaultPosition,
         const wxSize& size = wxDefaultSize,