diff --git a/Library/Homebrew/cmd/commands.rb b/Library/Homebrew/cmd/commands.rb
index 30034ec200..d7734e1327 100644
--- a/Library/Homebrew/cmd/commands.rb
+++ b/Library/Homebrew/cmd/commands.rb
@@ -38,6 +38,7 @@ module Homebrew
 
   def external_commands
     paths.flat_map { |p| Dir["#{p}/brew-*"] }.
+      select { |f| File.executable?(f) }.
       map { |f| File.basename(f, ".rb")[5..-1] }.
       reject { |f| f =~ /\./ }.
       sort