diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 7d90db0445..ae7bb34fa9 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -838,7 +838,7 @@ module Homebrew
         deleted_formulae = []
         kegs.each do |keg|
           keg_name = keg.name
-          deleted_formulae << keg_name if Formulary.tap_paths(keg_name).size != 1
+          deleted_formulae << keg_name if Formulary.tap_paths(keg_name).blank?
         end
         return if deleted_formulae.blank?