diff --git a/Library/Homebrew/cmd/doctor.rb b/Library/Homebrew/cmd/doctor.rb
index ad8892baab..480af7b7a2 100644
--- a/Library/Homebrew/cmd/doctor.rb
+++ b/Library/Homebrew/cmd/doctor.rb
@@ -1023,7 +1023,7 @@ def check_for_unlinked_but_not_keg_only
     if not rack.directory?
       true
     elsif not (HOMEBREW_REPOSITORY/"Library/LinkedKegs"/rack.basename).directory?
-      Formula.factory(rack.basename).keg_only? rescue nil
+      Formula.factory(rack.basename.to_s).keg_only? rescue nil
     else
       true
     end