diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index cb78221fd6..d553846e3c 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -395,7 +395,7 @@ class Formula
       raise LoadError
     end
 
-    raise NameError if klass.superclass != Formula
+    raise NameError if !klass.ancestors.include? Formula
 
     return klass.new(name) if install_type == :from_name
     return klass.new(name, path.to_s)