diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 274dc90effc4..11f3c4c46f6e 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -204,7 +204,7 @@ def constantize(camel_cased_word) #:nodoc:
 
       names.inject(Object) do |constant, name|
         candidate = constant.const_get(name)
-        if constant.const_defined?(name, false) || !Object.const_defined?(name)
+        if constant.const_defined?(name, false) || constant == Object || !Object.const_defined?(name)
           candidate
         else
           # Go down the ancestors to check it it's owned
diff --git a/activesupport/test/constantize_test_cases.rb b/activesupport/test/constantize_test_cases.rb
index 908f9e9a3793..470213e9bda6 100644
--- a/activesupport/test/constantize_test_cases.rb
+++ b/activesupport/test/constantize_test_cases.rb
@@ -12,6 +12,16 @@ class Gas
   end
 end
 
+class Object
+  module AddtlGlobalConstants
+    class Case
+      class Dice
+      end
+    end
+  end
+  include AddtlGlobalConstants
+end
+
 module ConstantizeTestCases
   def run_constantize_tests_on
     assert_nothing_raised { assert_equal Ace::Base::Case, yield("Ace::Base::Case") }
@@ -19,8 +29,12 @@ def run_constantize_tests_on
     assert_nothing_raised { assert_equal Ace::Base::Case::Dice, yield("Ace::Base::Case::Dice") }
     assert_nothing_raised { assert_equal Ace::Base::Fase::Dice, yield("Ace::Base::Fase::Dice") }
     assert_nothing_raised { assert_equal Ace::Gas::Case, yield("Ace::Gas::Case") }
+    assert_nothing_raised { assert_equal Case::Dice, yield("Case::Dice") }
+    assert_nothing_raised { assert_equal Case::Dice, yield("Object::Case::Dice") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("ConstantizeTestCases") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("::ConstantizeTestCases") }
+    assert_nothing_raised { assert_equal Object, yield("") }
+    assert_nothing_raised { assert_equal Object, yield("::") }
     assert_raise(NameError) { yield("UnknownClass") }
     assert_raise(NameError) { yield("UnknownClass::Ace") }
     assert_raise(NameError) { yield("UnknownClass::Ace::Base") }
@@ -38,8 +52,12 @@ def run_safe_constantize_tests_on
     assert_nothing_raised { assert_equal Ace::Base::Case::Dice, yield("Ace::Base::Case::Dice") }
     assert_nothing_raised { assert_equal Ace::Base::Fase::Dice, yield("Ace::Base::Fase::Dice") }
     assert_nothing_raised { assert_equal Ace::Gas::Case, yield("Ace::Gas::Case") }
+    assert_nothing_raised { assert_equal Case::Dice, yield("Case::Dice") }
+    assert_nothing_raised { assert_equal Case::Dice, yield("Object::Case::Dice") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("ConstantizeTestCases") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("::ConstantizeTestCases") }
+    assert_nothing_raised { assert_equal Object, yield("") }
+    assert_nothing_raised { assert_equal Object, yield("::") }
     assert_nothing_raised { assert_equal nil, yield("UnknownClass") }
     assert_nothing_raised { assert_equal nil, yield("UnknownClass::Ace") }
     assert_nothing_raised { assert_equal nil, yield("UnknownClass::Ace::Base") }