diff --git a/flask/testing.py b/flask/testing.py
index 782b40f6..bdd3860f 100644
--- a/flask/testing.py
+++ b/flask/testing.py
@@ -15,6 +15,7 @@ from __future__ import with_statement
 from contextlib import contextmanager
 from werkzeug.test import Client, EnvironBuilder
 from flask import _request_ctx_stack
+from urlparse import urlparse
 
 
 def make_test_environ_builder(app, path='/', base_url=None, *args, **kwargs):
@@ -22,9 +23,12 @@ def make_test_environ_builder(app, path='/', base_url=None, *args, **kwargs):
     http_host = app.config.get('SERVER_NAME')
     app_root = app.config.get('APPLICATION_ROOT')
     if base_url is None:
-        base_url = 'http://%s/' % (http_host or 'localhost')
+        url = urlparse(path)
+        base_url = 'http://%s/' % (url.netloc or http_host or 'localhost')
         if app_root:
             base_url += app_root.lstrip('/')
+        if url.netloc:
+            path = url.path
     return EnvironBuilder(path, base_url, *args, **kwargs)
 
 
diff --git a/flask/testsuite/testing.py b/flask/testsuite/testing.py
index 0e6feb60..92e3f267 100644
--- a/flask/testsuite/testing.py
+++ b/flask/testsuite/testing.py
@@ -198,7 +198,46 @@ class TestToolsTestCase(FlaskTestCase):
         self.assert_equal(called, [None, None])
 
 
+class SubdomainTestCase(FlaskTestCase):
+
+    def setUp(self):
+        self.app = flask.Flask(__name__)
+        self.app.config['SERVER_NAME'] = 'example.com'
+        self.client = self.app.test_client()
+
+        self._ctx = self.app.test_request_context()
+        self._ctx.push()
+
+    def tearDown(self):
+        if self._ctx is not None:
+            self._ctx.pop()
+
+    def test_subdomain(self):
+        @self.app.route('/', subdomain='<company_id>')
+        def view(company_id):
+            return company_id
+
+        url = flask.url_for('view', company_id='xxx')
+        response = self.client.get(url)
+
+        self.assertEquals(200, response.status_code)
+        self.assertEquals('xxx', response.data)
+
+
+    def test_nosubdomain(self):
+        @self.app.route('/<company_id>')
+        def view(company_id):
+            return company_id
+
+        url = flask.url_for('view', company_id='xxx')
+        response = self.client.get(url)
+
+        self.assertEquals(200, response.status_code)
+        self.assertEquals('xxx', response.data)
+
+
 def suite():
     suite = unittest.TestSuite()
     suite.addTest(unittest.makeSuite(TestToolsTestCase))
+    suite.addTest(unittest.makeSuite(SubdomainTestCase))
     return suite