diff --git a/lib/data_mapper/validation/rule/uniqueness.rb b/lib/data_mapper/validation/rule/uniqueness.rb
index 6ae184d4..d5dd1412 100644
--- a/lib/data_mapper/validation/rule/uniqueness.rb
+++ b/lib/data_mapper/validation/rule/uniqueness.rb
@@ -46,8 +46,9 @@ def valid?(resource)
             opts[subject] = resource.__send__(subject)
           }
 
+          property = resource.model.properties[attribute_name]
           other_resource = DataMapper.repository(resource.repository.name) do
-            resource.model.first(opts)
+            property.model.first(opts)
           end
 
           return true if other_resource.nil?
diff --git a/spec/fixtures/corporate_world.rb b/spec/fixtures/corporate_world.rb
index 37710ed3..eb495707 100644
--- a/spec/fixtures/corporate_world.rb
+++ b/spec/fixtures/corporate_world.rb
@@ -17,11 +17,24 @@ class Department
         include DataMapper::Resource
 
         property :id, Serial
+
+        property :type, Discriminator
+
         property :name, String, :unique_index => true
 
         validates_uniqueness_of :name
       end
 
+      class SpecialDepartment < Department
+        property :special_id, String
+        validates_uniqueness_of :special_id
+      end
+
+      class VerySpecialDepartment < Department
+        property :special_id, String
+        validates_uniqueness_of :special_id
+      end
+
       class User
         include DataMapper::Resource
 
diff --git a/spec/integration/uniqueness_validator/uniqueness_validator_spec.rb b/spec/integration/uniqueness_validator/uniqueness_validator_spec.rb
index b88db31a..593581bc 100644
--- a/spec/integration/uniqueness_validator/uniqueness_validator_spec.rb
+++ b/spec/integration/uniqueness_validator/uniqueness_validator_spec.rb
@@ -28,6 +28,54 @@
     end
   end
 
+  describe 'DataMapper::Validations::Fixtures::SpecialDepartment' do
+    before :all do
+      DataMapper::Validations::Fixtures::Department.destroy!
+
+      DataMapper::Validations::Fixtures::Department.create(:name => "HR").should be_saved
+    end
+
+    describe "with a duplicate name" do
+      before do
+        @model = DataMapper::Validations::Fixtures::SpecialDepartment.new(:name => "HR")
+      end
+
+      it_should_behave_like "invalid model"
+    end
+  end
+
+  describe 'DataMapper::Validations::Fixtures::SpecialDepartment' do
+    before :all do
+      DataMapper::Validations::Fixtures::Department.destroy!
+
+      DataMapper::Validations::Fixtures::SpecialDepartment.create(:name => "HR", :special_id => "1234").should be_saved
+    end
+
+    describe "with a duplicate special_id" do
+      before do
+        @model = DataMapper::Validations::Fixtures::SpecialDepartment.new(:name => "Other Dept.", :special_id => "1234")
+      end
+
+      it_should_behave_like "invalid model"
+    end
+  end
+
+  describe 'DataMapper::Validations::Fixtures::VerySpecialDepartment' do
+    before :all do
+      DataMapper::Validations::Fixtures::Department.destroy!
+
+      DataMapper::Validations::Fixtures::SpecialDepartment.create(:name => "HR", :special_id => "1234").should be_saved
+    end
+
+    describe "with a special_id also used by a SpecialDepartment" do
+      before do
+        @model = DataMapper::Validations::Fixtures::VerySpecialDepartment.new(:name => "Some Very Special Other Dept.", :special_id => "1234")
+      end
+
+      it_should_behave_like "valid model"
+    end
+  end
+
   describe 'DataMapper::Validations::Fixtures::Organisation' do
     before :all do
       DataMapper::Validations::Fixtures::Organisation.destroy!