diff --git a/harmonyqml/backend/model/list_model.py b/harmonyqml/backend/model/list_model.py
index 83ffe620..0b386f28 100644
--- a/harmonyqml/backend/model/list_model.py
+++ b/harmonyqml/backend/model/list_model.py
@@ -78,8 +78,10 @@ class ListModel(QAbstractListModel):
     def _convert_new_value(self, value: NewItem) -> ListItem:
         def convert() -> ListItem:
             if self._data and isinstance(value, Mapping):
-                assert set(value.keys()) <= set(self.roles), \
-                       f"{value}: must have all these keys: {self.roles}"
+                if not set(value.keys()) <= set(self.roles):
+                    raise ValueError(
+                        f"{value}: must have all these keys: {self.roles}"
+                    )
 
                 return type(self._data[0])(**value)
 
diff --git a/harmonyqml/backend/signal_manager.py b/harmonyqml/backend/signal_manager.py
index 3f67932a..4d144b31 100644
--- a/harmonyqml/backend/signal_manager.py
+++ b/harmonyqml/backend/signal_manager.py
@@ -124,7 +124,8 @@ class SignalManager(QObject):
                   inviter:    Inviter   = None,
                   left_event: LeftEvent = None) -> None:
 
-        assert not (inviter and left_event)
+        if (inviter and left_event):
+            raise ValueError()
 
         model     = self.backend.models.rooms[client.userId]
         no_update = []