diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index e1f9fc9ecc..68bd6d806b 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -279,6 +279,8 @@ module ActionDispatch
               if args.size < path_params_size
                 path_params -= controller_options.keys
                 path_params -= result.keys
+              else
+                path_params = path_params.dup
               end
               inner_options.each_key do |key|
                 path_params.delete(key)
diff --git a/actionpack/test/dispatch/routing/route_set_test.rb b/actionpack/test/dispatch/routing/route_set_test.rb
index ace35dda53..d6ecbda092 100644
--- a/actionpack/test/dispatch/routing/route_set_test.rb
+++ b/actionpack/test/dispatch/routing/route_set_test.rb
@@ -138,6 +138,15 @@ module ActionDispatch
         assert_equal "/a/users/1", url_helpers.user_path(1, foo: "a")
       end
 
+      test "implicit path components consistently return the same result" do
+        draw do
+          resources :users, to: SimpleApp.new("foo#index")
+        end
+        assert_equal "/users/1.json", url_helpers.user_path(1, :json)
+        assert_equal "/users/1.json", url_helpers.user_path(1, format: :json)
+        assert_equal "/users/1.json", url_helpers.user_path(1, :json)
+      end
+
       private
         def draw(&block)
           @set.draw(&block)