diff --git a/src/viewport.cpp b/src/viewport.cpp
index 82e6a4a205..84f78bf8d7 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -4392,7 +4392,7 @@ void MarkViewportDirty(Viewport * const vp, int left, int top, int right, int bo
 
 	uint x = std::max<int>(0, UnScaleByZoomLower(left, vp->zoom) - vp->dirty_block_left_margin) >> vp->GetDirtyBlockWidthShift();
 	uint y = UnScaleByZoomLower(top, vp->zoom) >> vp->GetDirtyBlockHeightShift();
-	uint w = (std::max<int>(0, UnScaleByZoomLower(right, vp->zoom) - 1 - vp->dirty_block_left_margin) >> vp->GetDirtyBlockWidthShift()) + 1 - x;
+	uint w = (std::max<int>(0, UnScaleByZoom(right, vp->zoom) - 1 - vp->dirty_block_left_margin) >> vp->GetDirtyBlockWidthShift()) + 1 - x;
 	uint h = ((UnScaleByZoom(bottom, vp->zoom) - 1) >> vp->GetDirtyBlockHeightShift()) + 1 - y;
 
 	uint column_skip = vp->dirty_blocks_per_column - h;