diff --git a/Library/Homebrew/cmd/sh.rb b/Library/Homebrew/cmd/sh.rb
index 82fcc968d8655524eb98b02c7a85e5c7122d80b0..d05af5bfd002ae25ff4bb17db3354ffad85dc07e 100644
--- a/Library/Homebrew/cmd/sh.rb
+++ b/Library/Homebrew/cmd/sh.rb
@@ -6,7 +6,7 @@ module Homebrew extend self
     ENV.activate_extensions!
 
     if superenv?
-      ENV.x11 = true
+      ENV.x11 = MacOS::X11.installed?
       ENV.deps = Formula.installed.select{|f| f.keg_only? and f.opt_prefix.directory? }.map(&:name)
     end
     ENV.setup_build_environment