diff --git a/src/govoplan_poll/backend/service.py b/src/govoplan_poll/backend/service.py
index fe12c66..1752e3f 100644
--- a/src/govoplan_poll/backend/service.py
+++ b/src/govoplan_poll/backend/service.py
@@ -483,7 +483,8 @@ def transition_poll(
     elif action == "close":
         poll.closed_at = now
     elif action == "decide":
-        assert decision_option is not None
+        if decision_option is None:
+            raise PollError("A decide transition requires a poll option")
         poll.decided_option_id = decision_option.id
         poll.decided_at = now
         if poll.closed_at is None:
diff --git a/src/govoplan_poll/backend/transitions.py b/src/govoplan_poll/backend/transitions.py
index f56c8f1..718f857 100644
--- a/src/govoplan_poll/backend/transitions.py
+++ b/src/govoplan_poll/backend/transitions.py
@@ -137,7 +137,8 @@ class PollTransitionEngine:
                 raise ValueError("Archived poll has no valid status to restore")
             else:
                 target_status = archived_from_status
-        assert target_status is not None
+        if target_status is None:
+            raise ValueError(f"Poll transition {action!r} did not resolve a target status")
         return PollTransitionPlan(action=action, from_status=current_status, to_status=target_status)
 
     def available_actions(