diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index cfd3b9fb38a9d3f3ea192bbffbc45525909d6590..9ed3579318cd9a7ff948ee8f1632b52ada3caaf2 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Ensure that validates_uniqueness_of works with with_scope. Closes #9235. [nik.wakelin, cavalle]
+
 * Partial updates include only unsaved attributes. Off by default; set YourClass.partial_updates = true to enable.  [Jeremy Kemper]
 
 * Removing unnecessary uses_tzinfo helper from tests, given that TZInfo is now bundled [Geoff Buesing]
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index 5e2f710db65513a76f0b3bba39a3ff4f5a3fa1bc..72c48d1e2a0c89f1c13a64029b8cf0697866a977 100755
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -654,13 +654,15 @@ def validates_uniqueness_of(*attr_names)
             condition_params << record.send(:id)
           end
 
-          results = connection.select_all(
-            construct_finder_sql(
-              :select     => "#{attr_name}",
-              :from       => "#{finder_class.quoted_table_name}",
-              :conditions => [condition_sql, *condition_params]
+          results = finder_class.with_exclusive_scope do
+            connection.select_all(
+              construct_finder_sql(
+                :select     => "#{attr_name}",
+                :from       => "#{finder_class.quoted_table_name}",
+                :conditions => [condition_sql, *condition_params]
+              )
             )
-          )
+          end
 
           unless results.length.zero?
             found = true
diff --git a/activerecord/test/cases/validations_test.rb b/activerecord/test/cases/validations_test.rb
index d0b4902bceefad0d7c881bc73fd0d7a1945cf967..1bcd72c71fda26c68b44b2729ebff62313c71bf7 100755
--- a/activerecord/test/cases/validations_test.rb
+++ b/activerecord/test/cases/validations_test.rb
@@ -467,6 +467,16 @@ def test_validate_uniqueness_with_non_standard_table_names
     assert i1.errors.on(:value), "Should not be empty"
   end
 
+  def test_validates_uniqueness_inside_with_scope
+    Topic.validates_uniqueness_of(:title)
+
+    Topic.with_scope(:find => { :conditions => { :author_name => "David" } }) do
+      t1 = Topic.new("title" => "I'm unique!", "author_name" => "Mary")
+      assert t1.save
+      t2 = Topic.new("title" => "I'm unique!", "author_name" => "David")
+      assert !t2.valid?
+    end
+  end
 
   def test_validate_straight_inheritance_uniqueness
     w1 = IneptWizard.create(:name => "Rincewind", :city => "Ankh-Morpork")