1 files changed, 6 insertions, 0 deletions
diff --git a/Library/Homebrew/cmd/install.rb b/Library/Homebrew/cmd/install.rb
index 4b2711994..07942f64e 100644
--- a/Library/Homebrew/cmd/install.rb
+++ b/Library/Homebrew/cmd/install.rb
@@ -9,6 +9,12 @@ module Homebrew extend self
       raise "No available formula for #{name}\n#{msg}" if msg
     end unless ARGV.force?
 
+    ARGV.formulae.each do |f|
+      if File.directory? HOMEBREW_REPOSITORY/"Library/LinkedKegs/#{f.name}"
+        raise "#{f} already installed\nTry: brew upgrade #{f}"
+      end
+    end
+
     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.