diff --git a/lib/rubygems.rb b/lib/rubygems.rb
index 270352501b..dbb32b220f 100644
--- a/lib/rubygems.rb
+++ b/lib/rubygems.rb
@@ -1217,7 +1217,7 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
 
     def register_default_spec(spec)
       extended_require_paths = spec.require_paths.map {|f| f + "/"}
-      new_format = spec.require_paths.any? {|path| spec.files.any? {|f| f.start_with? path } }
+      new_format = extended_require_paths.any? {|path| spec.files.any? {|f| f.start_with? path } }
 
       if new_format
         prefix_group = extended_require_paths.join("|")
diff --git a/test/rubygems/test_gem.rb b/test/rubygems/test_gem.rb
index d64a253bbc..6b18bb9eb5 100644
--- a/test/rubygems/test_gem.rb
+++ b/test/rubygems/test_gem.rb
@@ -1750,6 +1750,18 @@ class TestGem < Gem::TestCase
     assert_nil              Gem.find_unresolved_default_spec("README")
   end
 
+  def test_register_default_spec_old_style_with_folder_starting_with_lib
+    Gem.clear_default_specs
+
+    old_style = Gem::Specification.new do |spec|
+      spec.files = ["libexec/bundle", "foo.rb", "bar.rb"]
+    end
+
+    Gem.register_default_spec old_style
+
+    assert_equal old_style, Gem.find_unresolved_default_spec("foo.rb")
+  end
+
   def test_use_gemdeps
     gem_deps_file = 'gem.deps.rb'.tap(&Gem::UNTAINT)
     spec = util_spec 'a', 1