diff --git a/neo/core/regionofinterest.py b/neo/core/regionofinterest.py
index 3de9b624f..da7ed0409 100644
--- a/neo/core/regionofinterest.py
+++ b/neo/core/regionofinterest.py
@@ -28,7 +28,8 @@ def _get_obj(self):
         return self.image_sequence
 
     def _set_obj(self, value):
-        assert isinstance(value, ImageSequence)
+        if not isinstance(value, ImageSequence):
+            raise TypeError(f"Value must be ImageSequence, not of type: {type(value)}")
         self.image_sequence = value
 
     obj = property(fget=_get_obj, fset=_set_obj)