diff --git a/flask/__init__.py b/flask/__init__.py
index 54bfedda..f35ef328 100644
--- a/flask/__init__.py
+++ b/flask/__init__.py
@@ -23,7 +23,8 @@ from .config import Config
 from .helpers import url_for, jsonify, json_available, flash, \
     send_file, send_from_directory, get_flashed_messages, \
     get_template_attribute, make_response, safe_join
-from .globals import current_app, g, request, session, _request_ctx_stack
+from .globals import current_app, g, request, session, _request_ctx_stack, \
+     _app_ctx_stack
 from .ctx import has_request_context
 from .module import Module
 from .blueprints import Blueprint
diff --git a/flask/helpers.py b/flask/helpers.py
index 26be5e30..b86ce158 100644
--- a/flask/helpers.py
+++ b/flask/helpers.py
@@ -200,6 +200,9 @@ def url_for(endpoint, **values):
     """
     appctx = _app_ctx_stack.top
     reqctx = _request_ctx_stack.top
+    if appctx is None:
+        raise RuntimeError('Attempted to generate a URL with the application '
+                           'context being pushed.  This has to be executed ')
 
     # If request specific information is available we have some extra
     # features that support "relative" urls.
@@ -225,6 +228,11 @@ def url_for(endpoint, **values):
     # the urls external by default.
     else:
         url_adapter = appctx.url_adapter
+        if url_adapter is None:
+            raise RuntimeError('Application was not able to create a URL '
+                               'adapter for request independent URL generation. '
+                               'You might be able to fix this by setting '
+                               'the SERVER_NAME config variable.')
         external = values.pop('_external', True)
 
     anchor = values.pop('_anchor', None)
diff --git a/flask/testsuite/appctx.py b/flask/testsuite/appctx.py
index 2c198047..c60dbc67 100644
--- a/flask/testsuite/appctx.py
+++ b/flask/testsuite/appctx.py
@@ -18,7 +18,7 @@ from flask.testsuite import FlaskTestCase
 
 class AppContextTestCase(FlaskTestCase):
 
-    def test_basic_support(self):
+    def test_basic_url_generation(self):
         app = flask.Flask(__name__)
         app.config['SERVER_NAME'] = 'localhost'
         app.config['PREFERRED_URL_SCHEME'] = 'https'
@@ -31,6 +31,28 @@ class AppContextTestCase(FlaskTestCase):
             rv = flask.url_for('index')
             self.assert_equal(rv, 'https://localhost/')
 
+    def test_url_generation_requires_server_name(self):
+        app = flask.Flask(__name__)
+        with app.app_context():
+            with self.assert_raises(RuntimeError):
+                flask.url_for('index')
+
+    def test_url_generation_without_context_fails(self):
+        with self.assert_raises(RuntimeError):
+            flask.url_for('index')
+
+    def test_request_context_means_app_context(self):
+        app = flask.Flask(__name__)
+        with app.test_request_context():
+            self.assert_equal(flask.current_app._get_current_object(), app)
+        self.assert_equal(flask._app_ctx_stack.top, None)
+
+    def test_app_context_provides_current_app(self):
+        app = flask.Flask(__name__)
+        with app.app_context():
+            self.assert_equal(flask.current_app._get_current_object(), app)
+        self.assert_equal(flask._app_ctx_stack.top, None)
+
 
 def suite():
     suite = unittest.TestSuite()