diff --git a/scripts/calibrate_ask.py b/scripts/calibrate_ask.py
index 3ecdb13..6ca8582 100644
--- a/scripts/calibrate_ask.py
+++ b/scripts/calibrate_ask.py
@@ -109,8 +109,8 @@ def build_filters(args: argparse.Namespace) -> tuple[str, dict[str, Any]]:
     clauses = [
         "(:source IS NULL OR source = :source)",
         "(:prompt_version IS NULL OR prompt_version = :prompt_version)",
-        "(:since IS NULL OR created_at >= :since::timestamptz)",
-        "(:until IS NULL OR created_at < :until::timestamptz)",
+        "(:since IS NULL OR created_at >= CAST(:since AS TIMESTAMPTZ))",
+        "(:until IS NULL OR created_at < CAST(:until AS TIMESTAMPTZ))",
     ]
     params: dict[str, Any] = {
         "source": args.source,