diff --git a/locust/test/test_web.py b/locust/test/test_web.py
index 80f9cd7e87..b660555528 100644
--- a/locust/test/test_web.py
+++ b/locust/test/test_web.py
@@ -348,6 +348,9 @@ def t(self):
         self.assertEqual(self.environment.host, "https://localhost")
         self.assertListEqual(["User1", "User2"], response.json()["user_classes"])
 
+        self.assertIsNotNone(self.environment.locustfile, 'verify locustfile is not empty')
+        self.assertEqual(self.environment.locustfile, "User1,User2", "Verify locustfile variable used in web ui title")
+
         # stop
         gevent.sleep(1)
         response = requests.get("http://127.0.0.1:%i/stop" % self.web_port)
diff --git a/locust/web.py b/locust/web.py
index 17eb11c22e..c692099a7a 100644
--- a/locust/web.py
+++ b/locust/web.py
@@ -555,6 +555,9 @@ def _update_shape_class(self, shape_class_name):
 
     def _update_user_classes(self, user_classes):
         self.environment.user_classes = list(user_classes.values())
+        # populate the locustfile which used in web ui title only
+        if self.environment.locustfile is None:
+            self.environment.locustfile = ",".join(self.environment.user_classes_by_name.keys())
 
         # Validating UserClasses
         self.environment._remove_user_classes_with_weight_zero()