diff --git a/Library/Contributions/examples/brew-missing.rb b/Library/Contributions/examples/brew-missing.rb
index 2fac4186d4..21a0c071e5 100755
--- a/Library/Contributions/examples/brew-missing.rb
+++ b/Library/Contributions/examples/brew-missing.rb
@@ -11,6 +11,8 @@ def installed_brews
 end
 
 def main
+  return unless HOMEBREW_CELLAR.exist?
+
   # Names of outdated brews; they count as installed.
   outdated = Homebrew.outdated_brews.collect{ |b| b.name }