diff --git a/Library/Homebrew/caveats.rb b/Library/Homebrew/caveats.rb
index 584904791e..926614d0a0 100644
--- a/Library/Homebrew/caveats.rb
+++ b/Library/Homebrew/caveats.rb
@@ -95,6 +95,7 @@ class Caveats
           s << "    launchctl load #{plist_link}"
         end
       end
+      s << '' << "WARNING: launchctl will fail when run under tmux."
     end
     s.join("\n") unless s.empty?
   end