diff --git a/nglview/tests/test_widget.py b/nglview/tests/test_widget.py
index bfcd0691..9f0db547 100644
--- a/nglview/tests/test_widget.py
+++ b/nglview/tests/test_widget.py
@@ -88,9 +88,14 @@
 
 
 def get_mocked_traj():
-    class MockedTraj(nv.Structure):
+    class MockedTraj(nv.Structure, nv.Trajectory):
         def __init__(self):
-            self.n_frames = 10
+            nv.Structure.__init__(self)
+            nv.Trajectory.__init__(self)
+
+        @property
+        def n_frames(self):
+            return 10
 
         def get_coordinates(self, frame):
             return np.random.rand(10, 3, 3)
diff --git a/nglview/widget.py b/nglview/widget.py
index da9ae991..864c4ed5 100644
--- a/nglview/widget.py
+++ b/nglview/widget.py
@@ -691,7 +691,7 @@ def set_coordinates(self, arr_dict, movie_making=False,
     def _on_frame_changed(self, change):
         """set and send coordinates at current frame
         """
-        self._set_coordinates(self.frame)
+        self._set_coordinates(change['new'])
 
     def clear(self, *args, **kwargs):
         '''shortcut of `clear_representations`