diff -r 8e5787506b59 src/pkg/image/gif/writer.go
--- a/src/pkg/image/gif/writer.go	Tue Apr 15 15:52:23 2014 -0400
+++ b/src/pkg/image/gif/writer.go	Tue Apr 15 18:21:41 2014 -0400
@@ -233,7 +233,9 @@
 	e.writeByte(uint8(litWidth)) // LZW Minimum Code Size.
 
 	lzww := lzw.NewWriter(blockWriter{e: e}, lzw.LSB, litWidth)
-	_, e.err = lzww.Write(pm.Pix)
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		_, e.err = lzww.Write(pm.Pix[y*pm.Stride : y*pm.Stride+b.Dx()])
+	}
 	if e.err != nil {
 		lzww.Close()
 		return