diff --git a/mercurial/hgweb/request.py b/mercurial/hgweb/request.py
--- a/mercurial/hgweb/request.py
+++ b/mercurial/hgweb/request.py
@@ -222,7 +222,7 @@
     # root. We also exclude its path components from PATH_INFO when resolving
     # the dispatch path.
 
-    apppath = env['SCRIPT_NAME']
+    apppath = env.get('SCRIPT_NAME', '')
 
     if env.get('REPO_NAME'):
         if not apppath.endswith('/'):
diff --git a/tests/test-wsgirequest.py b/tests/test-wsgirequest.py
new file mode 100644
--- /dev/null
+++ b/tests/test-wsgirequest.py
@@ -0,0 +1,255 @@
+from __future__ import absolute_import, print_function
+
+import unittest
+
+from mercurial.hgweb import (
+    request as requestmod,
+)
+
+DEFAULT_ENV = {
+    r'REQUEST_METHOD': r'GET',
+    r'SERVER_NAME': r'testserver',
+    r'SERVER_PORT': r'80',
+    r'SERVER_PROTOCOL': r'http',
+    r'wsgi.version': (1, 0),
+    r'wsgi.url_scheme': r'http',
+    r'wsgi.input': None,
+    r'wsgi.errors': None,
+    r'wsgi.multithread': False,
+    r'wsgi.multiprocess': True,
+    r'wsgi.run_once': False,
+}
+
+def parse(env, bodyfh=None, extra=None):
+    env = dict(env)
+    env.update(extra or {})
+
+    return requestmod.parserequestfromenv(env, bodyfh)
+
+class ParseRequestTests(unittest.TestCase):
+    def testdefault(self):
+        r = parse(DEFAULT_ENV)
+        self.assertEqual(r.url, b'http://testserver')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.urlscheme, b'http')
+        self.assertEqual(r.method, b'GET')
+        self.assertIsNone(r.remoteuser)
+        self.assertIsNone(r.remotehost)
+        self.assertEqual(r.apppath, b'')
+        self.assertEqual(r.dispatchparts, [])
+        self.assertEqual(r.dispatchpath, b'')
+        self.assertFalse(r.havepathinfo)
+        self.assertIsNone(r.reponame)
+        self.assertEqual(r.querystring, b'')
+        self.assertEqual(len(r.qsparams), 0)
+        self.assertEqual(len(r.headers), 0)
+
+    def testcustomport(self):
+        r = parse(DEFAULT_ENV, extra={
+            r'SERVER_PORT': r'8000',
+        })
+
+        self.assertEqual(r.url, b'http://testserver:8000')
+        self.assertEqual(r.baseurl, b'http://testserver:8000')
+        self.assertEqual(r.advertisedurl, b'http://testserver:8000')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver:8000')
+
+        r = parse(DEFAULT_ENV, extra={
+            r'SERVER_PORT': r'4000',
+            r'wsgi.url_scheme': r'https',
+        })
+
+        self.assertEqual(r.url, b'https://testserver:4000')
+        self.assertEqual(r.baseurl, b'https://testserver:4000')
+        self.assertEqual(r.advertisedurl, b'https://testserver:4000')
+        self.assertEqual(r.advertisedbaseurl, b'https://testserver:4000')
+
+    def testhttphost(self):
+        r = parse(DEFAULT_ENV, extra={
+            r'HTTP_HOST': r'altserver',
+        })
+
+        self.assertEqual(r.url, b'http://altserver')
+        self.assertEqual(r.baseurl, b'http://altserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+
+    def testscriptname(self):
+        r = parse(DEFAULT_ENV, extra={
+            r'SCRIPT_NAME': r'',
+        })
+
+        self.assertEqual(r.url, b'http://testserver')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'')
+        self.assertEqual(r.dispatchparts, [])
+        self.assertEqual(r.dispatchpath, b'')
+        self.assertFalse(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'SCRIPT_NAME': r'/script',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/script')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/script')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/script')
+        self.assertEqual(r.dispatchparts, [])
+        self.assertEqual(r.dispatchpath, b'')
+        self.assertFalse(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'SCRIPT_NAME': r'/multiple words',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/multiple%20words')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/multiple%20words')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/multiple words')
+        self.assertEqual(r.dispatchparts, [])
+        self.assertEqual(r.dispatchpath, b'')
+        self.assertFalse(r.havepathinfo)
+
+    def testpathinfo(self):
+        r = parse(DEFAULT_ENV, extra={
+            r'PATH_INFO': r'',
+        })
+
+        self.assertEqual(r.url, b'http://testserver')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'')
+        self.assertEqual(r.dispatchparts, [])
+        self.assertEqual(r.dispatchpath, b'')
+        self.assertTrue(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'PATH_INFO': r'/pathinfo',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/pathinfo')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/pathinfo')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'')
+        self.assertEqual(r.dispatchparts, [b'pathinfo'])
+        self.assertEqual(r.dispatchpath, b'pathinfo')
+        self.assertTrue(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'PATH_INFO': r'/one/two/',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/one/two/')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/one/two/')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'')
+        self.assertEqual(r.dispatchparts, [b'one', b'two'])
+        self.assertEqual(r.dispatchpath, b'one/two')
+        self.assertTrue(r.havepathinfo)
+
+    def testscriptandpathinfo(self):
+        r = parse(DEFAULT_ENV, extra={
+            r'SCRIPT_NAME': r'/script',
+            r'PATH_INFO': r'/pathinfo',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/script/pathinfo')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/script/pathinfo')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/script')
+        self.assertEqual(r.dispatchparts, [b'pathinfo'])
+        self.assertEqual(r.dispatchpath, b'pathinfo')
+        self.assertTrue(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'SCRIPT_NAME': r'/script1/script2',
+            r'PATH_INFO': r'/path1/path2',
+        })
+
+        self.assertEqual(r.url,
+                         b'http://testserver/script1/script2/path1/path2')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl,
+                         b'http://testserver/script1/script2/path1/path2')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/script1/script2')
+        self.assertEqual(r.dispatchparts, [b'path1', b'path2'])
+        self.assertEqual(r.dispatchpath, b'path1/path2')
+        self.assertTrue(r.havepathinfo)
+
+        r = parse(DEFAULT_ENV, extra={
+            r'HTTP_HOST': r'hostserver',
+            r'SCRIPT_NAME': r'/script',
+            r'PATH_INFO': r'/pathinfo',
+        })
+
+        self.assertEqual(r.url, b'http://hostserver/script/pathinfo')
+        self.assertEqual(r.baseurl, b'http://hostserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/script/pathinfo')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/script')
+        self.assertEqual(r.dispatchparts, [b'pathinfo'])
+        self.assertEqual(r.dispatchpath, b'pathinfo')
+        self.assertTrue(r.havepathinfo)
+
+    def testreponame(self):
+        """REPO_NAME path components get stripped from URL."""
+        r = parse(DEFAULT_ENV, extra={
+            r'REPO_NAME': r'repo',
+            r'PATH_INFO': r'/path1/path2'
+        })
+
+        self.assertEqual(r.url, b'http://testserver/path1/path2')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/path1/path2')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/repo')
+        self.assertEqual(r.dispatchparts, [b'path1', b'path2'])
+        self.assertEqual(r.dispatchpath, b'path1/path2')
+        self.assertTrue(r.havepathinfo)
+        self.assertEqual(r.reponame, b'repo')
+
+        r = parse(DEFAULT_ENV, extra={
+            r'REPO_NAME': r'repo',
+            r'PATH_INFO': r'/repo/path1/path2',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/repo/path1/path2')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl, b'http://testserver/repo/path1/path2')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/repo')
+        self.assertEqual(r.dispatchparts, [b'path1', b'path2'])
+        self.assertEqual(r.dispatchpath, b'path1/path2')
+        self.assertTrue(r.havepathinfo)
+        self.assertEqual(r.reponame, b'repo')
+
+        r = parse(DEFAULT_ENV, extra={
+            r'REPO_NAME': r'prefix/repo',
+            r'PATH_INFO': r'/prefix/repo/path1/path2',
+        })
+
+        self.assertEqual(r.url, b'http://testserver/prefix/repo/path1/path2')
+        self.assertEqual(r.baseurl, b'http://testserver')
+        self.assertEqual(r.advertisedurl,
+                         b'http://testserver/prefix/repo/path1/path2')
+        self.assertEqual(r.advertisedbaseurl, b'http://testserver')
+        self.assertEqual(r.apppath, b'/prefix/repo')
+        self.assertEqual(r.dispatchparts, [b'path1', b'path2'])
+        self.assertEqual(r.dispatchpath, b'path1/path2')
+        self.assertTrue(r.havepathinfo)
+        self.assertEqual(r.reponame, b'prefix/repo')
+
+if __name__ == '__main__':
+    import silenttestrunner
+    silenttestrunner.main(__name__)