diff --git a/cmd/webp-manual-test/main.go b/cmd/webp-manual-test/main.go
index 8357f94..c041e21 100644
--- a/cmd/webp-manual-test/main.go
+++ b/cmd/webp-manual-test/main.go
@@ -1,3 +1,12 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+//
+// This build tag means that "go install golang.org/x/image/..." doesn't
+// install this manual test. Use "go run main.go" to explicitly run it.
+
 // Program webp-manual-test checks that the Go WEBP library's decodings match
 // the C WEBP library's.
 package main // import "golang.org/x/image/cmd/webp-manual-test"