diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 60c9fa65ac..7e62349222 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -649,8 +649,8 @@ class Formula
 
     HOMEBREW_CELLAR.subdirs.map do |rack|
       begin
-        Formulary.factory(rack.basename.to_s)
-      rescue FormulaUnavailableError
+        Formulary.from_rack(rack)
+      rescue FormulaUnavailableError, TapFormulaAmbiguityError
       end
     end.compact
   end