lib/usable.rb in usable-3.7.0 vs lib/usable.rb in usable-3.7.1

@@ -74,9 +74,10 @@
     Usable.copy_usables(self, base)
     super
   end
 
   def extended(base)
+    return if base === self
     base.extend(Usable) unless base.respond_to?(:usables)
     Usable.copy_usables(self, base)
     super
   end