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')
diff --git a/Lib/urlparse.py b/Lib/urlparse.py
index 4ac9867..a019a7b 100644
--- a/Lib/urlparse.py
+++ b/Lib/urlparse.py
@@ -256,14 +256,9 @@
     if path[:1] == '/':
         return urlunparse((scheme, netloc, path,
                            params, query, fragment))
-    if not path:
+    if not path and not params:
         path = bpath
-        if not params:
-            params = bparams
-        else:
-            path = path[:-1]
-            return urlunparse((scheme, netloc, path,
-                                params, query, fragment))
+        params = bparams
         if not query:
             query = bquery
         return urlunparse((scheme, netloc, path,
diff --git a/Misc/NEWS b/Misc/NEWS
index 5504796..aca1fbb 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -21,6 +21,8 @@
 
 Library
 -------
+- Issue #9721: Fix the behavior of urljoin when the relative url starts with a
+  ';' character. Patch by Wes Chow.
 
 - Issue #10714: Limit length of incoming request in http.server to 65536 bytes
   for security reasons.  Initial patch by Ross Lagerwall.