--- a/web/test/unittest_views_json.py	Wed Apr 15 22:48:20 2015 +0200
+++ b/web/test/unittest_views_json.py	Thu Jun 18 18:22:55 2015 +0200
@@ -43,10 +43,11 @@
 
     def test_json_rsetexport_with_jsonp(self):
         with self.admin_access.web_request() as req:
-            req.form.update({'callback': 'foo',
-                             'rql': 'Any GN,COUNT(X) GROUPBY GN ORDERBY GN '
+            req.form.update({'callback': u'foo',
+                             'rql': u'Any GN,COUNT(X) GROUPBY GN ORDERBY GN '
                              'WHERE X in_group G, G name GN'})
             data = self.ctrl_publish(req, ctrl='jsonp')
+            self.assertIsInstance(data, str)
             self.assertEqual(req.headers_out.getRawHeaders('content-type'), ['application/javascript'])
             # because jsonp anonymizes data, only 'guests' group should be found
             self.assertEqual(data, 'foo(%s)' % self.res_jsonp_data)

--- a/web/views/json.py	Wed Apr 15 22:48:20 2015 +0200
+++ b/web/views/json.py	Thu Jun 18 18:22:55 2015 +0200
@@ -60,11 +60,11 @@
     def _get_json_data(self, rset):
         json_data = super(JsonpController, self).publish(rset)
         if 'callback' in self._cw.form: # jsonp
-            json_padding = self._cw.form['callback']
-            # use ``application/javascript`` is ``callback`` parameter is
-            # provided, let ``application/json`` otherwise
+            json_padding = self._cw.form['callback'].encode('ascii')
+            # use ``application/javascript`` if ``callback`` parameter is
+            # provided, keep ``application/json`` otherwise
             self._cw.set_content_type('application/javascript')
-            json_data = '%s(%s)' % (json_padding, json_data)
+            json_data = b'%s(%s)' % (json_padding, json_data)
         return json_data