diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index de49750..bef4281 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -106,7 +106,9 @@ module ActiveSupport
       # unknown.
       def constantize(camel_cased_word)
         names = camel_cased_word.split('::')
-        names.shift if names.empty? || names.first.empty?
+
+        raise NameError, "empty constant name" if names.empty?
+        names.shift if names.first.empty?
 
         constant = Object
         names.each do |name|
@@ -117,7 +119,9 @@ module ActiveSupport
     else
       def constantize(camel_cased_word) #:nodoc:
         names = camel_cased_word.split('::')
-        names.shift if names.empty? || names.first.empty?
+
+        raise NameError, "empty constant name" if names.empty?
+        names.shift if names.first.empty?
 
         constant = Object
         names.each do |name|
@@ -148,4 +152,4 @@ module ActiveSupport
       end
     end
   end
-end
\ No newline at end of file
+end
diff --git a/activesupport/test/inflector_test.rb b/activesupport/test/inflector_test.rb
index 60714a1..01ccd67 100644
--- a/activesupport/test/inflector_test.rb
+++ b/activesupport/test/inflector_test.rb
@@ -200,6 +200,7 @@ class InflectorTest < Test::Unit::TestCase
     assert_raise(NameError) { ActiveSupport::Inflector.constantize("UnknownClass") }
     assert_raise(NameError) { ActiveSupport::Inflector.constantize("An invalid string") }
     assert_raise(NameError) { ActiveSupport::Inflector.constantize("InvalidClass\n") }
+    assert_raise(NameError) { ActiveSupport::Inflector.constantize("") }
   end
 
   def test_constantize_does_lexical_lookup