188,190c188,190
<       worker ct stride ptr = do let ptr2 = ptr `advancePtr` (2 * w)
<                                 fillSeg a ch ptr ptr2
<                                 worker (ct - 1) stride ptr2
---
>       worker ct stride ptr = do
>                                 fillSeg a ch ptr $ ptr `advancePtr` (2 * w)
>                                 worker (ct - 1) stride $ ptr `plusPtr` stride