diff --git a/flask/testing.py b/flask/testing.py
index 612b4d4d..757e20cc 100644
--- a/flask/testing.py
+++ b/flask/testing.py
@@ -57,7 +57,7 @@ class FlaskClient(Client):
             raise RuntimeError('Session transactions only make sense '
                                'with cookies enabled.')
         app = self.application
-        environ_overrides = kwargs.pop('environ_overrides', {})
+        environ_overrides = kwargs.setdefault('environ_overrides', {})
         self.cookie_jar.inject_wsgi(environ_overrides)
         outer_reqctx = _request_ctx_stack.top
         with app.test_request_context(*args, **kwargs) as c:
diff --git a/flask/testsuite/testing.py b/flask/testsuite/testing.py
index 32867c3f..5ee147f9 100644
--- a/flask/testsuite/testing.py
+++ b/flask/testsuite/testing.py
@@ -59,6 +59,9 @@ class TestToolsTestCase(FlaskTestCase):
                 self.assert_equal(len(sess), 1)
             rv = c.get('/')
             self.assert_equal(rv.data, '[42]')
+            with c.session_transaction() as sess:
+                self.assert_equal(len(sess), 1)
+                self.assert_equal(sess['foo'], [42])
 
     def test_session_transactions_no_null_sessions(self):
         app = flask.Flask(__name__)