diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
index 8244017..c5764c5 100644
--- a/Lib/test/test_urlparse.py
+++ b/Lib/test/test_urlparse.py
@@ -295,6 +295,9 @@
         #self.checkJoin(RFC3986_BASE, 'http:g','http:g') # strict parser
         self.checkJoin(RFC3986_BASE, 'http:g','http://a/b/c/g') # relaxed parser
 
+        # Test for issue9721
+        self.checkJoin('http://a/b/c/de', ';x','http://a/b/c/;x')
+
     def test_urljoins(self):
         self.checkJoin(SIMPLE_BASE, 'g:h','g:h')
         self.checkJoin(SIMPLE_BASE, 'http:g','http://a/b/c/g')