2 files changed, 16 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 942b4fa9bb..76c23df541 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -93,6 +93,18 @@ module ActiveModel
       @details  = other.details.dup
     end
 
+    # Merges the errors from <tt>other</tt>.
+    #
+    # other - The ActiveModel::Errors instance.
+    #
+    # Examples
+    #
+    #   person.errors.merge!(other)
+    def merge!(other)
+      @messages.merge!(other.messages) { |_, ary1, ary2| ary1 + ary2 }
+      @details.merge!(other.details) { |_, ary1, ary2| ary1 + ary2 }
+    end
+
     # Clear the error messages.
     #
     #   person.errors.full_messages # => ["name cannot be nil"]
diff --git a/activemodel/lib/active_model/type/date_time.rb b/activemodel/lib/active_model/type/date_time.rb
index 5cb0077e45..8ad0daa9a6 100644
--- a/activemodel/lib/active_model/type/date_time.rb
+++ b/activemodel/lib/active_model/type/date_time.rb
@@ -10,6 +10,10 @@ module ActiveModel
         :datetime
       end
 
+      def serialize(value)
+        super(cast(value))
+      end
+
       private
 
         def cast_value(value)