diff --git a/lib/ransack/nodes/grouping.rb b/lib/ransack/nodes/grouping.rb
index 3e38a8c..6835618 100644
--- a/lib/ransack/nodes/grouping.rb
+++ b/lib/ransack/nodes/grouping.rb
@@ -180,10 +180,15 @@ module Ransack
 
       def strip_predicate_and_index(str)
         string = str.split(/\(/).first
+        string = strip_before_type_cast(string)
         Predicate.detect_and_strip_from_string!(string)
         string
       end
 
+      def strip_before_type_cast(str)
+        str.split("_before_type_cast").first
+      end
+
     end
   end
 end
\ No newline at end of file
diff --git a/spec/blueprints/notes.rb b/spec/blueprints/notes.rb
index f143114..f6702ca 100644
--- a/spec/blueprints/notes.rb
+++ b/spec/blueprints/notes.rb
@@ -1,3 +1,5 @@
 Note.blueprint do
   note
+  notable_type { "Article" }
+  notable_id
 end
\ No newline at end of file
diff --git a/spec/ransack/helpers/form_builder_spec.rb b/spec/ransack/helpers/form_builder_spec.rb
index b00cd8e..7b8fc41 100644
--- a/spec/ransack/helpers/form_builder_spec.rb
+++ b/spec/ransack/helpers/form_builder_spec.rb
@@ -7,6 +7,7 @@ module Ransack
       router = ActionDispatch::Routing::RouteSet.new
       router.draw do
         resources :people
+        resources :notes
         get ':controller(/:action(/:id(.:format)))'
       end
 
@@ -132,6 +133,22 @@ module Ransack
           end
         end
       end
+
+      context 'fields used in polymorphic relations as search attributes in form' do
+        before do
+          @controller.view_context.search_form_for Note.search do |f|
+            @f = f
+          end
+        end
+        it 'accepts poly_id field' do
+          html = @f.text_field(:notable_id_eq)
+          html.should match /id=\"q_notable_id_eq\"/
+        end
+        it 'accepts poly_type field' do
+          html = @f.text_field(:notable_type_eq)
+          html.should match /id=\"q_notable_type_eq\"/
+        end
+      end
     end
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 77d9173..b9dd2ec 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -20,6 +20,7 @@ Sham.define do
   only_admin  { Faker::Lorem.words(3).join(' ') }
   only_search { Faker::Lorem.words(3).join(' ') }
   only_sort   { Faker::Lorem.words(3).join(' ') }
+  notable_id  { |id| id }
 end
 
 RSpec.configure do |config|