diff --git a/co-gahusb/app/store.py b/co-gahusb/app/store.py
index cc66279..00107e5 100644
--- a/co-gahusb/app/store.py
+++ b/co-gahusb/app/store.py
@@ -106,6 +106,8 @@ async def update_task(r, task_id, status, role, note=None):
     if status not in VALID_STATUS:
         raise ValueError(f"invalid status: {status}")
     key = TASK_PREFIX + str(task_id)
+    if not await r.exists(key):
+        return {"ok": False, "error": "not_found"}
     mapping = {"status": status}
     if note is not None:
         mapping["note"] = note
diff --git a/co-gahusb/tests/test_tasks.py b/co-gahusb/tests/test_tasks.py
index 03369cb..70a99a1 100644
--- a/co-gahusb/tests/test_tasks.py
+++ b/co-gahusb/tests/test_tasks.py
@@ -48,3 +48,9 @@ async def test_invalid_status_rejected(r):
     tid = (await store.create_task(r, "x", "FE", created_by="Producer"))["task_id"]
     with pytest.raises(ValueError):
         await store.update_task(r, tid, "bogus", "FE")
+
+
+async def test_update_nonexistent_task_returns_not_found(r):
+    res = await store.update_task(r, 999, "done", "FE")
+    assert res["ok"] is False
+    assert res["error"] == "not_found"