3 files changed, 37 insertions, 3 deletions
diff --git a/activemodel/lib/active_model/naming.rb b/activemodel/lib/active_model/naming.rb
index fc2abacb6d..2d580fd325 100644
--- a/activemodel/lib/active_model/naming.rb
+++ b/activemodel/lib/active_model/naming.rb
@@ -73,8 +73,10 @@ module ActiveModel
     # Returns an ActiveModel::Name object for module. It can be
     # used to retrieve all kinds of naming-related information.
     def model_name
-      namespace = self.parents.detect { |n| n.respond_to?(:_railtie) }
-      @_model_name ||= ActiveModel::Name.new(self, namespace)
+      @_model_name ||= begin
+        namespace = self.parents.detect { |n| n.respond_to?(:_railtie) }
+        ActiveModel::Name.new(self, namespace)
+      end
     end
 
     # Returns the plural class name of a record or class. Examples:
diff --git a/activemodel/lib/active_model/validations/confirmation.rb b/activemodel/lib/active_model/validations/confirmation.rb
index 2c8a840124..00df10cef0 100644
--- a/activemodel/lib/active_model/validations/confirmation.rb
+++ b/activemodel/lib/active_model/validations/confirmation.rb
@@ -10,7 +10,9 @@ module ActiveModel
       end
 
       def setup(klass)
-        klass.send(:attr_accessor, *attributes.map { |attribute| :"#{attribute}_confirmation" })
+        klass.send(:attr_accessor, *attributes.map do |attribute|
+          :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation")
+        end.compact)
       end
     end
 
diff --git a/activemodel/test/cases/callbacks_test.rb b/activemodel/test/cases/callbacks_test.rb
index 64dc7b5026..069d907fb2 100644
--- a/activemodel/test/cases/callbacks_test.rb
+++ b/activemodel/test/cases/callbacks_test.rb
@@ -81,4 +81,34 @@ class CallbacksTest < ActiveModel::TestCase
     assert !ModelCallbacks.respond_to?(:around_empty)
     assert !ModelCallbacks.respond_to?(:after_empty)
   end
+
+  class Violin
+    attr_reader :history
+    def initialize
+      @history = []
+    end
+    extend ActiveModel::Callbacks
+    define_model_callbacks :create
+    def callback1; self.history << 'callback1'; end
+    def callback2; self.history << 'callback2'; end
+    def create
+      _run_create_callbacks {}
+      self
+    end
+  end
+  class Violin1 < Violin
+    after_create :callback1, :callback2
+  end
+  class Violin2 < Violin
+    after_create :callback1
+    after_create :callback2
+  end
+
+  test "after_create callbacks with both callbacks declared in one line" do
+    assert_equal ["callback1", "callback2"], Violin1.new.create.history
+  end
+  test "after_create callbacks with both callbacks declared in differnt lines" do
+    assert_equal ["callback1", "callback2"], Violin2.new.create.history
+  end
+
 end