diff --git a/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb b/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb
index d4e6b5a1ac..a77da573fe 100644
--- a/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb
+++ b/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb
@@ -206,7 +206,7 @@ class Module
   #   Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]
   def mattr_accessor(*syms, &blk)
     mattr_reader(*syms, &blk)
-    mattr_writer(*syms, &blk)
+    mattr_writer(*syms)
   end
   alias :cattr_accessor :mattr_accessor
 end
diff --git a/activesupport/test/core_ext/module/attribute_accessor_test.rb b/activesupport/test/core_ext/module/attribute_accessor_test.rb
index 48f3cc579f..128c5e3d1a 100644
--- a/activesupport/test/core_ext/module/attribute_accessor_test.rb
+++ b/activesupport/test/core_ext/module/attribute_accessor_test.rb
@@ -76,4 +76,10 @@ class ModuleAttributeAccessorTest < ActiveSupport::TestCase
     assert_equal 'default_reader_value', @module.defr
     assert_equal 'default_writer_value', @module.class_variable_get('@@defw')
   end
+
+  def test_should_not_invoke_default_value_block_multiple_times
+    count = 0
+    @module.cattr_accessor(:defcount){ count += 1 }
+    assert_equal 1, count
+  end
 end