diff --git a/Library/Homebrew/cmd/upgrade.rb b/Library/Homebrew/cmd/upgrade.rb
index f27357764a..215ae3d146 100644
--- a/Library/Homebrew/cmd/upgrade.rb
+++ b/Library/Homebrew/cmd/upgrade.rb
@@ -9,6 +9,12 @@ end
 
 module Homebrew extend self
   def upgrade
+    if Process.uid.zero? and not File.stat(HOMEBREW_BREW_FILE).uid.zero?
+      # note we only abort if Homebrew is *not* installed as sudo and the user
+      # calls brew as root. The fix is to chown brew to root.
+      abort "Cowardly refusing to `sudo brew upgrade'"
+    end
+
     Homebrew.perform_preinstall_checks
 
     outdated = if ARGV.named.empty?