diff --git a/flask/testing.py b/flask/testing.py
index c4d18ca2..6ce96163 100644
--- a/flask/testing.py
+++ b/flask/testing.py
@@ -53,10 +53,12 @@ class FlaskClient(Client):
         :meth:`~flask.Flask.test_request_context` which are directly
         passed through.
         """
+        if self.cookie_jar is None:
+            raise RuntimeError('Session transactions only make sense '
+                               'with cookies enabled.')
         app = self.application
         environ_overrides = kwargs.pop('environ_overrides', {})
-        if self.cookie_jar is not None:
-            self.cookie_jar.inject_wsgi(environ_overrides)
+        self.cookie_jar.inject_wsgi(environ_overrides)
         outer_reqctx = _request_ctx_stack.top
         with app.test_request_context(*args, **kwargs) as c:
             sess = app.open_session(c.request)
@@ -80,9 +82,8 @@ class FlaskClient(Client):
             resp = app.response_class()
             if not app.session_interface.is_null_session(sess):
                 app.save_session(sess, resp)
-            if self.cookie_jar is not None:
-                headers = resp.get_wsgi_headers(c.request.environ)
-                self.cookie_jar.extract_wsgi(c.request.environ, headers)
+            headers = resp.get_wsgi_headers(c.request.environ)
+            self.cookie_jar.extract_wsgi(c.request.environ, headers)
 
     def open(self, *args, **kwargs):
         if self.context_preserved:
diff --git a/flask/testsuite/testing.py b/flask/testsuite/testing.py
index f665e12c..b7a71b1a 100644
--- a/flask/testsuite/testing.py
+++ b/flask/testsuite/testing.py
@@ -84,6 +84,18 @@ class TestToolsTestCase(FlaskTestCase):
             with c.session_transaction():
                 self.assert_(req is flask.request._get_current_object())
 
+    def test_session_transaction_needs_cookies(self):
+        app = flask.Flask(__name__)
+        app.testing = True
+        c = app.test_client(use_cookies=False)
+        try:
+            with c.session_transaction() as s:
+                pass
+        except RuntimeError, e:
+            self.assert_('cookies' in str(e))
+        else:
+            self.fail('Expected runtime error')
+
     def test_test_client_context_binding(self):
         app = flask.Flask(__name__)
         @app.route('/')