--- a/scripts/marionette.py
+++ b/scripts/marionette.py
@@ -429,16 +429,20 @@ class MarionetteTest(TestingMixin, Toolt
                     config_fmt_args['binary'] = os.path.join(binary_path, 'b2g-bin')
                 else:
                     # if b2g-bin cannot be found we must use just b2g
                     config_fmt_args['binary'] = os.path.join(binary_path, 'b2g')
 
             if self.config.get('this_chunk') and self.config.get('total_chunks'):
                 config_fmt_args['this_chunk'] = self.config.get('this_chunk')
                 config_fmt_args['total_chunks'] = self.config.get('total_chunks')
+            else:
+                # pass 1 as default so that the config option is honoured
+                config_fmt_args['this_chunk'] = 1
+                config_fmt_args['total_chunks'] = 1
 
             # Bug 1046694
             # using a different manifest if a specific gip-suite is specified
             # --type parameter depends on gip-suite
             if self.config.get('gip_suite'):
                 manifest = os.path.join(dirs['abs_gaiatest_dir'], 'gaiatest', 'tests', self.config.get('gip_suite'),
                                         'manifest.ini')
                 if self.config.get('gip_suite') == "functional":