diff --git a/src/net/http/sniff.go b/src/net/http/sniff.go
index 0d21b44a56..ecc65e4de6 100644
--- a/src/net/http/sniff.go
+++ b/src/net/http/sniff.go
@@ -107,8 +107,8 @@ var sniffSignatures = []sniffSig{
 		ct:   "audio/basic",
 	},
 	&maskedSig{
-		mask: []byte("OggS\x00"),
-		pat:  []byte("\x4F\x67\x67\x53\x00"),
+		mask: []byte("\xFF\xFF\xFF\xFF\xFF"),
+		pat:  []byte("OggS\x00"),
 		ct:   "application/ogg",
 	},
 	&maskedSig{
diff --git a/src/net/http/sniff_test.go b/src/net/http/sniff_test.go
index 38f3f8197e..24f1298e5d 100644
--- a/src/net/http/sniff_test.go
+++ b/src/net/http/sniff_test.go
@@ -45,7 +45,11 @@ var sniffTests = []struct {
 	{"WAV audio #1", []byte("RIFFb\xb8\x00\x00WAVEfmt \x12\x00\x00\x00\x06"), "audio/wave"},
 	{"WAV audio #2", []byte("RIFF,\x00\x00\x00WAVEfmt \x12\x00\x00\x00\x06"), "audio/wave"},
 	{"AIFF audio #1", []byte("FORM\x00\x00\x00\x00AIFFCOMM\x00\x00\x00\x12\x00\x01\x00\x00\x57\x55\x00\x10\x40\x0d\xf3\x34"), "audio/aiff"},
+
 	{"OGG audio", []byte("OggS\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x7e\x46\x00\x00\x00\x00\x00\x00\x1f\xf6\xb4\xfc\x01\x1e\x01\x76\x6f\x72"), "application/ogg"},
+	{"Must not match OGG", []byte("owow\x00"), "application/octet-stream"},
+	{"Must not match OGG", []byte("oooS\x00"), "application/octet-stream"},
+	{"Must not match OGG", []byte("oggS\x00"), "application/octet-stream"},
 
 	// Video types.
 	{"MP4 video", []byte("\x00\x00\x00\x18ftypmp42\x00\x00\x00\x00mp42isom<\x06t\xbfmdat"), "video/mp4"},