diff --git a/gpu/gpu.go b/gpu/gpu.go
index d8cc63a8..ea5a6b02 100644
--- a/gpu/gpu.go
+++ b/gpu/gpu.go
@@ -867,7 +867,7 @@ func (r *renderer) drawLayers(layers []opacityLayer, ops []imageOp) {
 			Min: l.place.Pos,
 			Max: l.place.Pos.Add(l.clip.Size()),
 		}
-		r.ctx.Viewport(v.Min.X, v.Min.Y, v.Max.X, v.Max.Y)
+		r.ctx.Viewport(v.Min.X, v.Min.Y, v.Dx(), v.Dy())
 		f := r.layerFBOs.fbos[fbo]
 		r.drawOps(true, l.clip.Min.Mul(-1), l.clip.Size(), ops[l.opStart:l.opEnd])
 		sr := f32.FRect(v)
@@ -1232,7 +1232,7 @@ func (r *renderer) prepareDrawOps(ops []imageOp) {
 	}
 }
 
-func (r *renderer) drawOps(isFBO bool, opOff image.Point, viewport image.Point, ops []imageOp) {
+func (r *renderer) drawOps(isFBO bool, opOff, viewport image.Point, ops []imageOp) {
 	var coverTex driver.Texture
 	for i := 0; i < len(ops); i++ {
 		img := ops[i]
diff --git a/gpu/internal/rendertest/refs/TestOpacity.png b/gpu/internal/rendertest/refs/TestOpacity.png
index 7ddf84ea..c7f7d5af 100644
Binary files a/gpu/internal/rendertest/refs/TestOpacity.png and b/gpu/internal/rendertest/refs/TestOpacity.png differ
diff --git a/gpu/internal/rendertest/render_test.go b/gpu/internal/rendertest/render_test.go
index fc5c7fa8..41478319 100644
--- a/gpu/internal/rendertest/render_test.go
+++ b/gpu/internal/rendertest/render_test.go
@@ -483,14 +483,14 @@ func TestGapsInPath(t *testing.T) {
 func TestOpacity(t *testing.T) {
 	run(t, func(ops *op.Ops) {
 		opc1 := paint.PushOpacity(ops, .3)
-		// Fill screen to exercize the glClear optimization.
+		// Fill screen to exercise the glClear optimization.
 		paint.FillShape(ops, color.NRGBA{R: 255, A: 255}, clip.Rect{Max: image.Pt(1024, 1024)}.Op())
 		opc2 := paint.PushOpacity(ops, .6)
 		paint.FillShape(ops, color.NRGBA{G: 255, A: 255}, clip.Rect{Min: image.Pt(20, 10), Max: image.Pt(64, 128)}.Op())
 		opc2.Pop()
 		opc1.Pop()
 		opc3 := paint.PushOpacity(ops, .6)
-		paint.FillShape(ops, color.NRGBA{G: 255, A: 255}, clip.Rect{Min: image.Pt(50+20, 10), Max: image.Pt(50+64, 128)}.Op())
+		paint.FillShape(ops, color.NRGBA{B: 255, A: 255}, clip.Ellipse(image.Rectangle{Min: image.Pt(20+20, 10), Max: image.Pt(50+64, 128)}).Op(ops))
 		opc3.Pop()
 	}, func(r result) {
 	})