diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index c19d4c7b32c682896d010209d6ea43059b085863..c339e9380812ecc1298c574ced2c9f88ee9e5772 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,5 +1,8 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*    Deprecates the compatibility method Module#local_constant_names,
+     use Module#local_constants instead (which returns symbols). *fxn*
+
 *    Deletes the compatibility method Module#method_names,
      use Module#methods from now on (which returns symbols). *fxn*
 
diff --git a/activesupport/lib/active_support/core_ext/module/introspection.rb b/activesupport/lib/active_support/core_ext/module/introspection.rb
index 1893a9cfa65385304ba29a92798657219c67a13a..743db47bac9398509fd05814a4e91aca9defc787 100644
--- a/activesupport/lib/active_support/core_ext/module/introspection.rb
+++ b/activesupport/lib/active_support/core_ext/module/introspection.rb
@@ -61,9 +61,19 @@ def local_constants #:nodoc:
     constants(false)
   end
 
-  # Returns the names of the constants defined locally rather than the
-  # constants themselves. See <tt>local_constants</tt>.
+  # *DEPRECATED*: Use +local_constants+ instead.
+  #
+  # Returns the names of the constants defined locally as strings.
+  #
+  #   module M
+  #     X = 1
+  #   end
+  #   M.local_constant_names # => ["X"]
+  #
+  # This method is useful for forward compatibility, since Ruby 1.8 returns
+  # constant names as strings, whereas 1.9 returns them as symbols.
   def local_constant_names
+    ActiveSupport::Deprecation.warn('Module#local_constant_names is deprecated, use Module#local_constants instead', caller)
     local_constants.map { |c| c.to_s }
   end
 end
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index e121e452a3f20fcfeeba94f7d4f54beea31190c3..2c5950edf51dc1f36f39b7b599408a05e401d53d 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -105,7 +105,7 @@ def new_constants
           next unless mod.is_a?(Module)
 
           # Get a list of the constants that were added
-          new_constants = mod.local_constant_names - original_constants
+          new_constants = mod.local_constants - original_constants
 
           # self[namespace] returns an Array of the constants that are being evaluated
           # for that namespace. For instance, if parent.rb requires child.rb, the first
@@ -133,7 +133,7 @@ def watch_namespaces(namespaces)
         namespaces.map do |namespace|
           module_name = Dependencies.to_constant_name(namespace)
           original_constants = Dependencies.qualified_const_defined?(module_name) ?
-            Inflector.constantize(module_name).local_constant_names : []
+            Inflector.constantize(module_name).local_constants : []
 
           watching << module_name
           @stack[module_name] << original_constants
diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb
index 950ef82a3c343ff073ecaae8a5b63a738392b217..09ca4e729624bfa10bfb70c61dbf3aec8ad7e39d 100644
--- a/activesupport/test/core_ext/module_test.rb
+++ b/activesupport/test/core_ext/module_test.rb
@@ -212,6 +212,12 @@ def test_parents
   def test_local_constants
     assert_equal %w(Constant1 Constant3), Ab.local_constants.sort.map(&:to_s)
   end
+
+  def test_local_constant_names
+    ActiveSupport::Deprecation.silence do
+      assert_equal %w(Constant1 Constant3), Ab.local_constant_names
+    end
+  end
 end
 
 module BarMethodAliaser
diff --git a/railties/guides/source/active_support_core_extensions.textile b/railties/guides/source/active_support_core_extensions.textile
index 7b3878d2229c910d50bc75043c6451f302efe5a9..bf8d328020147963e935a05520701375feaf0cc3 100644
--- a/railties/guides/source/active_support_core_extensions.textile
+++ b/railties/guides/source/active_support_core_extensions.textile
@@ -692,7 +692,8 @@ NOTE: Defined in +active_support/core_ext/module/introspection.rb+.
 
 h4. Constants
 
-The method +local_constants+ returns the names of the constants that have been defined in the receiver module:
+The method +local_constants+ returns the names of the constants that have been
+defined in the receiver module:
 
 <ruby>
 module X
@@ -708,7 +709,8 @@ X.local_constants    # => [:X1, :X2, :Y]
 X::Y.local_constants # => [:Y1, :X1]
 </ruby>
 
-The names are returned as symbols. The method +local_constant_names+ always returns strings.
+The names are returned as symbols. (The method +local_constant_names+ returns
+strings, but +local_constant_names+ is deprecated.)
 
 NOTE: Defined in +active_support/core_ext/module/introspection.rb+.