diff --git a/src/blackboard/db.py b/src/blackboard/db.py
index 4e09c40..f5b9c8d 100644
--- a/src/blackboard/db.py
+++ b/src/blackboard/db.py
@@ -169,7 +169,7 @@ _SCHEMA_STATEMENTS = [
     # observations
     """CREATE TABLE IF NOT EXISTS observations (
         id INTEGER PRIMARY KEY AUTOINCREMENT,
-        task_id TEXT NOT NULL REFERENCES tasks(id),
+        task_id TEXT REFERENCES tasks(id),
         observer TEXT NOT NULL,
         severity TEXT NOT NULL DEFAULT 'info' CHECK (severity IN ('blocking','warning','info','audit')),
         body TEXT NOT NULL,