diff --git a/draw/scale.go b/draw/scale.go
index 07cd20b..4d77764 100644
--- a/draw/scale.go
+++ b/draw/scale.go
@@ -410,9 +410,11 @@
 	if dstMask == nil {
 		return adr, nil
 	}
-	if r, ok := dstMask.(image.Rectangle); ok {
-		return adr.Intersect(r.Sub(dstMaskP)), nil
-	}
+	// TODO: enable this fast path once Go 1.5 is released, where an
+	// image.Rectangle implements image.Image.
+	// if r, ok := dstMask.(image.Rectangle); ok {
+	// 	return adr.Intersect(r.Sub(dstMaskP)), nil
+	// }
 	// TODO: clip to dstMask.Bounds() if the color model implies that out-of-bounds means 0 alpha?
 	return adr, dstMask
 }
diff --git a/draw/scale_test.go b/draw/scale_test.go
index d9265a1..cfa38a7 100644
--- a/draw/scale_test.go
+++ b/draw/scale_test.go
@@ -433,7 +433,9 @@
 		for _, dstMaskP := range dstMaskPs {
 			dstInside := mk(q, nil, image.Point{})
 			for _, wrap := range []bool{false, true} {
-				dstMask := image.Image(rect)
+				// TODO: replace "rectImage(rect)" with "rect" once Go 1.5 is
+				// released, where an image.Rectangle implements image.Image.
+				dstMask := image.Image(rectImage(rect))
 				if wrap {
 					dstMask = srcWrapper{dstMask}
 				}
@@ -463,6 +465,19 @@
 	}
 }
 
+// TODO: delete this wrapper type once Go 1.5 is released, where an
+// image.Rectangle implements image.Image.
+type rectImage image.Rectangle
+
+func (r rectImage) ColorModel() color.Model { return color.Alpha16Model }
+func (r rectImage) Bounds() image.Rectangle { return image.Rectangle(r) }
+func (r rectImage) At(x, y int) color.Color {
+	if (image.Point{x, y}).In(image.Rectangle(r)) {
+		return color.Opaque
+	}
+	return color.Transparent
+}
+
 // The fooWrapper types wrap the dst or src image to avoid triggering the
 // type-specific fast path implementations.
 type (