diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index d2684da9a1e1d0d8491f2c7a456b7b4b6866093f..e92ceb13620a1fd737e01c511bcb01159aa25045 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Object.subclasses_of includes anonymous subclasses.  [Jeremy Kemper]
+
 * Fixed that pluralizing an empty string should return the same empty string, not "s" #7720 [josh]
 
 * Added call to inspect on non-string classes for the logger #8533 [codahale]
diff --git a/activesupport/lib/active_support/core_ext/object/extending.rb b/activesupport/lib/active_support/core_ext/object/extending.rb
index 08159094104fa7b32e7f3e32bfbece936c4d2968..7c79d73f21873a6a2117f6445dacfa90649b2770 100644
--- a/activesupport/lib/active_support/core_ext/object/extending.rb
+++ b/activesupport/lib/active_support/core_ext/object/extending.rb
@@ -5,17 +5,21 @@ def remove_subclasses_of(*superclasses) #:nodoc:
 
   def subclasses_of(*superclasses) #:nodoc:
     subclasses = []
+
+    # Exclude this class unless it's a subclass of our supers and is defined.
+    # We check defined? in case we find a removed class that has yet to be
+    # garbage collected. This also fails for anonymous classes -- please
+    # submit a patch if you have a workaround.
     ObjectSpace.each_object(Class) do |k|
-      next unless # Exclude this class unless
-        superclasses.any? { |superclass| k < superclass } &&        # It *is* a subclass of our supers
-        eval("defined?(::#{k}) && ::#{k}.object_id == k.object_id") # It *is* defined
-          # Note that we check defined? in case we find a removed class that has
-          # yet to be garbage collected.
-      subclasses << k
+      if superclasses.any? { |superclass| k < superclass } &&
+        (k.name.blank? || eval("defined?(::#{k}) && ::#{k}.object_id == k.object_id"))
+        subclasses << k
+      end
     end
+
     subclasses
   end
-  
+
   def extended_by #:nodoc:
     ancestors = class << self; ancestors end
     ancestors.select { |mod| mod.class == Module } - [ Object, Kernel ]
diff --git a/activesupport/test/abstract_unit.rb b/activesupport/test/abstract_unit.rb
index fba9ff97b28950e469fd540d3206826657f48db3..791efb549afd863b3dc6b8721ad69339fd5e4178 100644
--- a/activesupport/test/abstract_unit.rb
+++ b/activesupport/test/abstract_unit.rb
@@ -6,6 +6,7 @@
 # Wrap tests that use Mocha and skip if unavailable.
 def uses_mocha(test_name)
   require 'rubygems'
+  gem 'mocha', '>= 0.5.5'
   require 'mocha'
   yield
 rescue LoadError
diff --git a/activesupport/test/core_ext/object_and_class_ext_test.rb b/activesupport/test/core_ext/object_and_class_ext_test.rb
index 1fbb853bc92d71a9d1a31a746387176f36baa04b..a23da097e99531b1faf71b1548f58e151bb49db5 100644
--- a/activesupport/test/core_ext/object_and_class_ext_test.rb
+++ b/activesupport/test/core_ext/object_and_class_ext_test.rb
@@ -97,7 +97,14 @@ def test_subclasses_of_with_multiple_roots
     classes = Object.subclasses_of(ClassI, ClassK)
     assert_equal %w(ClassJ Nested::ClassL), classes.collect(&:to_s).sort
   end
-  
+
+  def test_subclasses_of_doesnt_find_anonymous_classes
+    assert_equal [], Object.subclasses_of(Foo)
+    bar = Class.new(Foo)
+    assert_nothing_raised do
+      assert_equal [bar], Object.subclasses_of(Foo)
+    end
+  end
 end
 
 class ObjectTests < Test::Unit::TestCase