diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index ada5e39ead..e6257f8c4a 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -135,7 +135,7 @@ module ActionController
       end
     end
 
-    def self.custom_encoding_for(action, param) # :nodoc:
+    def self.action_encoding_template(action) # :nodoc:
       false
     end
 
diff --git a/actionpack/lib/action_controller/metal/parameter_encoding.rb b/actionpack/lib/action_controller/metal/parameter_encoding.rb
index d587772536..d6d33ad8c8 100644
--- a/actionpack/lib/action_controller/metal/parameter_encoding.rb
+++ b/actionpack/lib/action_controller/metal/parameter_encoding.rb
@@ -15,8 +15,10 @@ module ActionController
         @_parameter_encodings = Hash.new { |h, k| h[k] = {} }
       end
 
-      def custom_encoding_for(action, param) # :nodoc:
-        @_parameter_encodings[action.to_s][param.to_s]
+      def action_encoding_template(action) # :nodoc:
+        if @_parameter_encodings.has_key?(action.to_s)
+          @_parameter_encodings[action.to_s]
+        end
       end
 
       # Specify that a given action's parameters should all be encoded as
diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index 36b55c950c..08c9162316 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -76,7 +76,7 @@ module ActionDispatch
     PASS_NOT_FOUND = Class.new { # :nodoc:
       def self.action(_); self; end
       def self.call(_); [404, { "X-Cascade" => "pass" }, []]; end
-      def self.custom_encoding_for(action, param); nil; end
+      def self.action_encoding_template(action); false; end
     }
 
     def controller_class
diff --git a/actionpack/lib/action_dispatch/request/utils.rb b/actionpack/lib/action_dispatch/request/utils.rb
index 2985849527..f298cac9d1 100644
--- a/actionpack/lib/action_dispatch/request/utils.rb
+++ b/actionpack/lib/action_dispatch/request/utils.rb
@@ -80,20 +80,19 @@ module ActionDispatch
 
       class CustomParamEncoder # :nodoc:
         def self.encode(request, params, controller, action)
-          return params unless controller && controller.valid_encoding?
-
+          return params unless controller && controller.valid_encoding? && encoding_template = action_encoding_template(request, controller, action)
           params.except(:controller, :action).each do |key, value|
             ActionDispatch::Request::Utils.each_param_value(value) do |param|
-              if desired_encoding = custom_encoding_for(request, controller, action, key)
-                param.force_encoding(desired_encoding)
+              if encoding_template[key.to_s]
+                param.force_encoding(encoding_template[key.to_s])
               end
             end
           end
           params
         end
 
-        def self.custom_encoding_for(request, controller, action, param)
-          request.controller_class_for(controller).custom_encoding_for(action, param)
+        def self.action_encoding_template(request, controller, action) # :nodoc:
+          request.controller_class_for(controller).action_encoding_template(action)
         rescue MissingController
           nil
         end
diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index 96ea071531..44d45924e7 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -4607,6 +4607,21 @@ class TestInvalidUrls < ActionDispatch::IntegrationTest
       assert_response :ok
     end
   end
+
+  test "does not encode params besides id" do
+    with_routing do |set|
+      set.draw do
+        get "/foo/show(/:id)", to: "test_invalid_urls/foo#show"
+        get "/bar/show(/:id)", controller: "test_invalid_urls/foo", action: "show"
+      end
+
+      get "/foo/show/%E2%EF%BF%BD%A6?something_else=%E2%EF%BF%BD%A6"
+      assert_response :bad_request
+
+      get "/foo/show/%E2%EF%BF%BD%A6?something_else=%E2%EF%BF%BD%A6"
+      assert_response :bad_request
+    end
+  end
 end
 
 class TestOptionalRootSegments < ActionDispatch::IntegrationTest