diff --git a/src/msw/dc.cpp b/src/msw/dc.cpp
index 78f0fbb3f4..4ebdcc8140 100644
--- a/src/msw/dc.cpp
+++ b/src/msw/dc.cpp
@@ -2624,11 +2624,12 @@ static bool AlphaBlt(wxMSWDCImpl* dcDst,
             if ( data )
             {
                 wxAlphaPixelData::Iterator p(data);
-                for ( int old_y = 0; old_y < data.GetHeight(); old_y++ )
+                p.Offset(data, x, y);
+                for ( int yDst = 0; yDst < dstHeight; yDst++ )
                 {
                     wxAlphaPixelData::Iterator rowStart = p;
 
-                    for ( int old_x = 0; old_x < data.GetWidth(); old_x++ )
+                    for ( int xDst = 0; xDst < dstWidth; xDst++ )
                     {
                         // We choose to use wxALPHA_TRANSPARENT instead
                         // of perhaps more logical wxALPHA_OPAQUE here