diff --git a/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py b/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py
index 81b3a3d..e40e66d 100644
--- a/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py
+++ b/backend/alembic/versions/034_add_user_id_to_ntfy_sent.py
@@ -24,10 +24,14 @@ def upgrade() -> None:
         "fk_ntfy_sent_user_id", "ntfy_sent", "users",
         ["user_id"], ["id"], ondelete="CASCADE"
     )
+    # On fresh DB ntfy_sent may be empty — clean up NULLs just in case
+    op.execute("DELETE FROM ntfy_sent WHERE user_id IS NULL")
     op.alter_column("ntfy_sent", "user_id", nullable=False)
 
-    # Drop old unique constraint on notification_key alone
-    op.drop_constraint("ntfy_sent_notification_key_key", "ntfy_sent", type_="unique")
+    # Migration 022 created a unique INDEX (ix_ntfy_sent_notification_key), not a
+    # named unique CONSTRAINT. Drop the index; the new composite unique constraint
+    # below replaces it.
+    op.drop_index("ix_ntfy_sent_notification_key", table_name="ntfy_sent")
 
     # Create composite unique constraint (per-user dedup)
     op.create_unique_constraint(
@@ -39,8 +43,8 @@ def upgrade() -> None:
 def downgrade() -> None:
     op.drop_index("ix_ntfy_sent_user_id", table_name="ntfy_sent")
     op.drop_constraint("uq_ntfy_sent_user_key", "ntfy_sent", type_="unique")
-    op.create_unique_constraint(
-        "ntfy_sent_notification_key_key", "ntfy_sent", ["notification_key"]
+    op.create_index(
+        "ix_ntfy_sent_notification_key", "ntfy_sent", ["notification_key"], unique=True
     )
     op.drop_constraint("fk_ntfy_sent_user_id", "ntfy_sent", type_="foreignkey")
     op.drop_column("ntfy_sent", "user_id")