diff --git a/init.rb b/init.rb
index 6ad5881..238b5de 100644
--- a/init.rb
+++ b/init.rb
@@ -10,7 +10,7 @@ module ValidatesUrlFormatOf
     \A
     https?://                                                          # http:// or https://
     ([^\s:@]+:[^\s:@]*@)?                                              # optional username:pw@
-    ( ((#{ALNUM}+\.)*xn---*)?#{ALNUM}+([-.]#{ALNUM}+)*\.[a-z]{2,6}\.? |  # domain (including Punycode/IDN)...
+    ( ((#{ALNUM}+\.)*xn---*)?#{ALNUM}+([-.]#{ALNUM}+)*\.[a-z]{2,6}\.?(--#{ALNUM}*)? |  # domain (including Punycode/IDN)...
         #{IPv4_PART}(\.#{IPv4_PART}){3} )                              # or IPv4
     (:\d{1,5})?                                                        # optional port
     ([/?]\S*)?                                                         # optional /whatever or ?whatever
diff --git a/test/validates_url_format_of_test.rb b/test/validates_url_format_of_test.rb
index 05e31cb..bcb728e 100644
--- a/test/validates_url_format_of_test.rb
+++ b/test/validates_url_format_of_test.rb
@@ -70,6 +70,7 @@ def test_should_allow_valid_urls
       'http://www.xn--rksmrgs-5wao1o.nu',
       'http://foo.bar.xn--rksmrgs-5wao1o.nu',
       'https://www.xn----ylbbafnbqebomc7ds.com.gr',
+      'http://xn--80agkgigub5kqa.xn--p1ai',
       'http://example.com.',  # Explicit TLD root period
       'http://example.com./foo'
     ].each do |url|