+    if ( bitmap.Ok() && !size.IsFullySpecified() )
+    {
+        // in Mac OS X the bitmap buttons can have only one of the few standard
+        // sizes and if they don't, the OS rescales them automatically
+        // resulting in really ugly images, so centre the image in a square of
+        // standard size instead
+
+        // the supported sizes, sorted in decreasng order
+        static const int stdSizes[] = { 128, 48, 32, 16, 0 };
+
+        const int width = bitmap.GetWidth();
+        const int height = bitmap.GetHeight();
+
+        int n;
+        for ( n = 0; n < (int)WXSIZEOF(stdSizes); n++ )
+        {
+            const int sizeStd = stdSizes[n];
+            if ( width > sizeStd || height > sizeStd )
+            {
+                // it will become -1 if the bitmap is larger than the biggest
+                // supported size, this is intentional
+                n--;
+
+                break;
+            }
+        }
+
+        if ( n != -1 )
+        {
+            const int sizeStd = stdSizes[n];
+            if ( width != sizeStd || height != sizeStd )
+            {
+                wxASSERT_MSG( width <= sizeStd && height <= sizeStd,
+                              _T("bitmap shouldn't be cropped") );
+
+                m_bmpNormal.Create(sizeStd, sizeStd);
+                wxMemoryDC dcMem;
+                dcMem.SelectObject(m_bmpNormal);
+                dcMem.Clear();
+
+                dcMem.DrawBitmap(bitmap,
+                                 (sizeStd - width)/2, (sizeStd-height)/2,
+                                 true);
+            }
+        }
+        //else: let the system rescale the bitmap
+    }
+
+    if ( !m_bmpNormal.Ok() )
+        m_bmpNormal = bitmap;
+
+