diff --git a/Library/Homebrew/superenv.rb b/Library/Homebrew/superenv.rb
index dfa6b2610bc051911b7a5ed3e85b6ff4b9897ea0..1a665d00f4a09b75c4754e15cf80ccfe93d05f9f 100644
--- a/Library/Homebrew/superenv.rb
+++ b/Library/Homebrew/superenv.rb
@@ -25,6 +25,7 @@ rescue # blanket rescue because there are naked raises
   false
 end
 
+# Note that this block is guarded with `if superenv?`
 class << ENV
   attr_accessor :keg_only_deps, :deps, :x11
   alias_method :x11?, :x11