diff --git a/lib/cask/source/tapped.rb b/lib/cask/source/tapped.rb
index a36e51f6afe4e..e26472022ef94 100644
--- a/lib/cask/source/tapped.rb
+++ b/lib/cask/source/tapped.rb
@@ -4,6 +4,10 @@ def self.me?(query)
   end
 
   def self.path_for_query(query)
+    # Repeating Cask.all_titles is very slow for operations such as
+    # brew cask list, but memoizing the value might cause breakage
+    # elsewhere, given that installation and tap status is permitted
+    # to change during the course of an invocation.
     cask_with_tap = Cask.all_titles.find { |t| t.split('/').last == query.sub(/\.rb$/i,'') }
     if cask_with_tap
       user, repo, cask = cask_with_tap.split('/')