2 files changed, 13 insertions, 7 deletions
diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index 703aeec0a..b1a70c79d 100644
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -417,7 +417,10 @@ func writeImage(w io.Writer, m image.Image, cb int, level int) error {
 		}
 
 		// Apply the filter.
-		f := filter(&cr, pr, bpp)
+		f := ftNone
+		if level != zlib.NoCompression {
+			f = filter(&cr, pr, bpp)
+		}
 
 		// Write the compressed bytes.
 		if _, err := zw.Write(cr[f]); err != nil {
diff --git a/src/pkg/image/png/writer_test.go b/src/pkg/image/png/writer_test.go
index 6a872e274..d67a81569 100644
--- a/src/pkg/image/png/writer_test.go
+++ b/src/pkg/image/png/writer_test.go
@@ -81,20 +81,23 @@ func TestWriterLevels(t *testing.T) {
 	m := image.NewNRGBA(image.Rect(0, 0, 100, 100))
 
 	var b1, b2 bytes.Buffer
-	var e1, e2 Encoder
-
-	if err := e1.Encode(&b1, m); err != nil {
+	if err := (&Encoder{}).Encode(&b1, m); err != nil {
 		t.Fatal(err)
 	}
-
-	e2.CompressionLevel = NoCompression
-	if err := e2.Encode(&b2, m); err != nil {
+	noenc := &Encoder{CompressionLevel: NoCompression}
+	if err := noenc.Encode(&b2, m); err != nil {
 		t.Fatal(err)
 	}
 
 	if b2.Len() <= b1.Len() {
 		t.Error("DefaultCompression encoding was larger than NoCompression encoding")
 	}
+	if _, err := Decode(&b1); err != nil {
+		t.Error("cannot decode DefaultCompression")
+	}
+	if _, err := Decode(&b2); err != nil {
+		t.Error("cannot decode NoCompression")
+	}
 }
 
 func TestSubImage(t *testing.T) {