src/pkg/image/png/writer.go      |  5 ++---
 src/pkg/image/png/writer_test.go | 16 ++++++++++++++++

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index a03cc166510229633cfbe6b3c3f49e78b2038173..081d06bf57178c5babbd1f80893bb3368622ce95 100644
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -311,9 +311,8 @@ 				cr[0][3*x+2] = uint8(g >> 8)
 				cr[0][3*x+3] = uint8(b >> 8)
 			}
 		case cbP8:
-			for x := b.Min.X; x < b.Max.X; x++ {
-				cr[0][x+1] = paletted.ColorIndexAt(x, y)
-			}
+			rowOffset := y * paletted.Stride
+			copy(cr[0][b.Min.X+1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
 		case cbTCA8:
 			// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
 			for x := b.Min.X; x < b.Max.X; x++ {
diff --git a/src/pkg/image/png/writer_test.go b/src/pkg/image/png/writer_test.go
index 0fb7bebaed0ee61608b762bb1c739590e740256a..f218a5564bb0c103eeec4a9a6fe5f179a0a7b006 100644
--- a/src/pkg/image/png/writer_test.go
+++ b/src/pkg/image/png/writer_test.go
@@ -5,6 +5,7 @@
 package png
 
 import (
+	"bytes"
 	"fmt"
 	"image"
 	"io"
@@ -68,3 +69,18 @@ 			continue
 		}
 	}
 }
+
+func BenchmarkEncodePaletted(b *testing.B) {
+	b.StopTimer()
+	img := image.NewPaletted(640, 480,
+		[]image.Color{
+			image.RGBAColor{0, 0, 0, 255},
+			image.RGBAColor{255, 255, 255, 255},
+		})
+	b.StartTimer()
+	buffer := new(bytes.Buffer)
+	for i := 0; i < b.N; i++ {
+		buffer.Reset()
+		Encode(buffer, img)
+	}
+}