diff --git a/Formula/yarn.rb b/Formula/yarn.rb
index f2746843a2..66b6a40b2b 100644
--- a/Formula/yarn.rb
+++ b/Formula/yarn.rb
@@ -3,6 +3,11 @@ require "language/node"
 class Yarn < Formula
   desc "Javascript package manager"
   homepage "https://yarnpkg.com/"
+  # Note: If updating this to a newer version, please change the URL to the official
+  # yarnpkg.com download URL:
+  # url "https://yarnpkg.com/downloads/0.15.0/yarn-v0.15.0.tar.gz"
+  # This was not updated yet as Yarn 0.15.1 was an npm-specific release and is not available
+  # as a standalone tarball.
   url "https://registry.npmjs.org/yarn/-/yarn-0.15.1.tgz"
   sha256 "f99fd587e84987909d5f9e918b8fe524349fdc548e5bc5c380c8f8c0a70c6b87"
   head "https://github.com/yarnpkg/yarn.git"