diff --git a/tests/gateway/test_session_store_runtime_stale_guard.py b/tests/gateway/test_session_store_runtime_stale_guard.py
index 262d1a489bb..57f8c624bf2 100644
--- a/tests/gateway/test_session_store_runtime_stale_guard.py
+++ b/tests/gateway/test_session_store_runtime_stale_guard.py
@@ -49,6 +49,10 @@ def _db_returning(rows: dict) -> MagicMock:
     db.find_latest_gateway_session_for_peer.return_value = None
     db.reopen_session.return_value = None
     db.create_session.return_value = None
+    # No compression continuation → the tip is the session itself (identity),
+    # mirroring the real SessionDB.get_compression_tip. Without this a bare Mock
+    # would return a Mock the routing heal then assigns as session_id.
+    db.get_compression_tip.side_effect = lambda sid: sid
     return db