diff --git a/lib/friendly_id/base.rb b/lib/friendly_id/base.rb
index 5e10762f3..18195c8bf 100644
--- a/lib/friendly_id/base.rb
+++ b/lib/friendly_id/base.rb
@@ -249,7 +249,7 @@ def to_param
 
     # Clears slug on duplicate records when calling `dup`.
     def dup
-      super.tap { |duplicate| duplicate.slug = nil }
+      super.tap { |duplicate| duplicate.slug = nil if duplicate.respond_to?('slug=') }
     end
   end
 end