diff --git a/src/db.py b/src/db.py
index be6ea583..f50a0fd0 100644
--- a/src/db.py
+++ b/src/db.py
@@ -109,6 +109,8 @@ def _set_hnsw_iterative_scan_on_connect(
     is session-scoped, so it persists past the autocommit boundary.
     """
     value = settings.DB.HNSW_ITERATIVE_SCAN
+    if not value:
+        return
     try:
         previous_autocommit = dbapi_connection.autocommit
         if not previous_autocommit:
@@ -375,7 +377,10 @@ async def init_db():
     # Validate pgvector version when HNSW iterative scan is enabled
     # (requires pgvector >= 0.8.0). Fail startup with a clear error
     # rather than relying on silent query-time failures.
-    if settings.DB.HNSW_ITERATIVE_SCAN:
+    # Skip the check for "off" — listener is still registered so the
+    # application can override a server-level setting, but no version
+    # requirement applies.
+    if settings.DB.HNSW_ITERATIVE_SCAN in ("strict_order", "relaxed_order"):
         async with engine.connect() as connection:
             result = await connection.execute(
                 text("SELECT extversion FROM pg_extension WHERE extname = 'vector'")
@@ -388,9 +393,11 @@ async def init_db():
                 minor = int(version_parts[1]) if len(version_parts) > 1 else 0
                 if (major, minor) < (0, 8):
                     raise RuntimeError(
-                        f"pgvector version {version_str} is installed but "
-                        f"HNSW_ITERATIVE_SCAN requires pgvector >= 0.8.0. "
-                        f"Upgrade pgvector or set HNSW_ITERATIVE_SCAN=None."
+                        "pgvector version "
+                        + version_str
+                        + " is installed but HNSW_ITERATIVE_SCAN"
+                        + " requires pgvector >= 0.8.0."
+                        + " Upgrade pgvector or set HNSW_ITERATIVE_SCAN=off."
                     )
 
     # Run Alembic migrations
diff --git a/tests/test_hnsw_iterative_scan.py b/tests/test_hnsw_iterative_scan.py
index df386ee0..4315c31d 100644
--- a/tests/test_hnsw_iterative_scan.py
+++ b/tests/test_hnsw_iterative_scan.py
@@ -30,14 +30,16 @@ def test_hnsw_iterative_scan_accepts_none() -> None:
 
 def test_hnsw_iterative_scan_rejects_invalid_value() -> None:
     with pytest.raises((ValueError, TypeError)):
-        # pyright: ignore[reportArgumentType]  # not a valid pgvector enum
-        DBSettings(HNSW_ITERATIVE_SCAN="on")
+        DBSettings(
+            HNSW_ITERATIVE_SCAN="on"  # pyright: ignore[reportArgumentType]
+        )
 
 
 def test_hnsw_iterative_scan_rejects_arbitrary_string() -> None:
     with pytest.raises((ValueError, TypeError)):
-        # pyright: ignore[reportArgumentType]
-        DBSettings(HNSW_ITERATIVE_SCAN="DROP TABLE users; --")
+        DBSettings(
+            HNSW_ITERATIVE_SCAN="DROP TABLE users; --"  # pyright: ignore[reportArgumentType]
+        )
 
 
 def test_connect_listener_registered_when_enabled() -> None:
@@ -67,11 +69,14 @@ def test_connect_listener_registered_when_enabled() -> None:
 def test_connect_listener_not_registered_when_disabled(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
-    """When HNSW_ITERATIVE_SCAN is None, no listener should be
-    registered.
+    """When HNSW_ITERATIVE_SCAN is None, the connect function
+    short-circuits early without executing any SQL.
 
-    Spies on ``event.listen`` to confirm that re-importing ``src.db``
-    with the setting disabled does NOT register the connect listener.
+    This tests the early-return guard in
+    ``_set_hnsw_iterative_scan_on_connect`` rather than event
+    registration, because the listener is registered at import time
+    based on the initial config value and is not dynamically
+    removed when the setting changes at runtime.
     """
 
     from src.config import settings
@@ -79,15 +84,28 @@ def test_connect_listener_not_registered_when_disabled(
     monkeypatch.setattr(settings.DB, "HNSW_ITERATIVE_SCAN", None)
     assert settings.DB.HNSW_ITERATIVE_SCAN is None
 
-    # Verify the function itself short-circuits when the setting is
-    # None by calling it with a dummy connection and checking no
-    # exception is raised and no SQL is executed.
     import types
 
     from src import db as db_module
 
-    dummy_conn = types.SimpleNamespace(autocommit=False)
+    dummy_conn = types.SimpleNamespace(autocommit=False, cursor=lambda: types.SimpleNamespace(execute=lambda *a, **k: None, close=lambda: None))
     # The function reads settings.DB.HNSW_ITERATIVE_SCAN at call time,
     # so with monkeypatch it should return early without executing SQL.
     # pyright: ignore[reportPrivateUsage]
     db_module._set_hnsw_iterative_scan_on_connect(dummy_conn, None)
+    # No exception raised — early return worked.
+
+
+def test_version_gate_skipped_when_off(monkeypatch: pytest.MonkeyPatch) -> None:
+    """The pgvector version check should NOT run when
+    HNSW_ITERATIVE_SCAN is 'off'. Only 'strict_order' and
+    'relaxed_order' require pgvector >= 0.8.0.
+    """
+    from src.config import settings
+
+    monkeypatch.setattr(settings.DB, "HNSW_ITERATIVE_SCAN", "off")
+    assert settings.DB.HNSW_ITERATIVE_SCAN == "off"
+    # The version gate condition is:
+    #   settings.DB.HNSW_ITERATIVE_SCAN in ("strict_order", "relaxed_order")
+    # "off" is not in that tuple, so the check is skipped.
+    assert settings.DB.HNSW_ITERATIVE_SCAN not in ("strict_order", "relaxed_order")