diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index 84f755688e..345c34a190 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -49,12 +49,16 @@ begin
   end
 
   path = PATH.new(ENV["PATH"])
+  homebrew_path = PATH.new(ENV["HOMEBREW_PATH"])
 
   # Add contributed commands to PATH before checking.
-  path.append(Pathname.glob(Tap::TAP_DIRECTORY/"*/*/cmd"))
+  tap_cmds = Pathname.glob(Tap::TAP_DIRECTORY/"*/*/cmd")
+  path.append(tap_cmds)
+  homebrew_path.append(tap_cmds)
 
   # Add SCM wrappers.
   path.append(HOMEBREW_SHIMS_PATH/"scm")
+  homebrew_path.append(HOMEBREW_SHIMS_PATH/"scm")
 
   ENV["PATH"] = path
 
@@ -89,6 +93,9 @@ begin
     system(HOMEBREW_BREW_FILE, "uninstall", "--force", "brew-cask")
   end
 
+  # External commands expect a normal PATH
+  ENV["PATH"] = homebrew_path unless internal_cmd
+
   if internal_cmd
     Homebrew.send cmd.to_s.tr("-", "_").downcase
   elsif which "brew-#{cmd}"