diff --git a/ChangeLog b/ChangeLog
index 089d0cf30f..3e1dc9b5ce 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Aug 30 09:21:01 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/uri/ftp.rb (URI::FTP#initialize): raise InvalidURIError if "//"
+	  is not present [ruby-core:47344] [Bug #6945]
+
 Thu Aug 30 07:45:12 2012  Luis Lavena  <luislavena@gmail.com>
 
 	* test/ruby/test_file_exhaustive.rb: fix test introduced in r36811 for
diff --git a/lib/uri/ftp.rb b/lib/uri/ftp.rb
index 26e4bb8326..971684a545 100644
--- a/lib/uri/ftp.rb
+++ b/lib/uri/ftp.rb
@@ -135,6 +135,7 @@ module URI
     # +opaque+, +query+ and +fragment+, in that order.
     #
     def initialize(*arg)
+      raise InvalidURIError unless arg[5]
       arg[5] = arg[5].sub(/^\//,'').sub(/^%2F/,'/')
       super(*arg)
       @typecode = nil
diff --git a/test/uri/test_ftp.rb b/test/uri/test_ftp.rb
index 0d76c4497b..cc6843e60f 100644
--- a/test/uri/test_ftp.rb
+++ b/test/uri/test_ftp.rb
@@ -27,6 +27,10 @@ class TestFTP < Test::Unit::TestCase
     assert_equal('pass', url.password)
   end
 
+  def test_parse_invalid
+    assert_raise(InvalidURIError){URI.parse('ftp:example')}
+  end
+
   def test_paths
     # If you think what's below is wrong, please read RubyForge bug 2055,
     # RFC 1738 section 3.2.2, and RFC 2396.