diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 21453f5e9a..ef4834811c 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -1685,8 +1685,8 @@ MSG
             if include_readonly_attributes || (!include_readonly_attributes && !self.class.readonly_attributes.include?(name))
               value = read_attribute(name)
 
-              if value && ((self.class.serialized_attributes.has_key?(name) && (value.acts_like?(:date) || value.acts_like?(:time))) || value.is_a?(Hash) || value.is_a?(Array))
-                value = value.to_yaml
+              if value && self.class.serialized_attributes.key?(name)
+                value = YAML.dump value
               end
               attrs[self.class.arel_table[name]] = value
             end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index cc3d123cea..cb1d2ae421 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -17,6 +17,11 @@ module ActiveRecord
         table = finder_class.unscoped
 
         table_name   = record.class.quoted_table_name
+
+        if value && record.class.serialized_attributes.key?(attribute.to_s)
+          value = YAML.dump value
+        end
+
         sql, params  = mount_sql_and_params(finder_class, table_name, attribute, value)
 
         relation = table.where(sql, *params)
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 07b06e15a3..dcb1da7d91 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -909,9 +909,13 @@ class BasicsTest < ActiveRecord::TestCase
   MyObject = Struct.new :attribute1, :attribute2
 
   def test_serialized_attribute
+    Topic.serialize("content", MyObject)
+
     myobj = MyObject.new('value1', 'value2')
     topic = Topic.create("content" => myobj)
-    Topic.serialize("content", MyObject)
+    assert_equal(myobj, topic.content)
+
+    topic.reload
     assert_equal(myobj, topic.content)
   end