diff --git a/Library/brew.rb b/Library/brew.rb
index ae9b37d6bb..4874aeb967 100755
--- a/Library/brew.rb
+++ b/Library/brew.rb
@@ -100,7 +100,8 @@ begin
   end
 
   # Add contributed commands to PATH before checking.
-  ENV['PATH'] += ":#{HOMEBREW_CONTRIB}/cmd"
+  ENV['PATH'] += "#{File::PATH_SEPARATOR}#{HOMEBREW_CONTRIB}/cmd"
+
   if require? HOMEBREW_REPOSITORY/"Library/Homebrew/cmd"/cmd
     Homebrew.send cmd.to_s.gsub('-', '_').downcase
   elsif which "brew-#{cmd}"