diff --git a/scripts/calibrate_ask.py b/scripts/calibrate_ask.py
index 6ca8582..dba167a 100644
--- a/scripts/calibrate_ask.py
+++ b/scripts/calibrate_ask.py
@@ -104,21 +104,23 @@ def build_filters(args: argparse.Namespace) -> tuple[str, dict[str, Any]]:
     """공통 WHERE 절 SQL + 바인딩 파라미터.
 
     조건 4가지: source, prompt_version, since, until.
-    None 인 항목은 IS NULL 로 무력화 (SQL CASE 회피, 단순 OR 패턴).
+    None 인 항목은 WHERE 에 포함하지 않음 (asyncpg 이 None param 의 타입 추론 실패 회피).
     """
-    clauses = [
-        "(:source IS NULL OR source = :source)",
-        "(:prompt_version IS NULL OR prompt_version = :prompt_version)",
-        "(: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,
-        "prompt_version": args.prompt_version,
-        "since": args.since,
-        "until": args.until,
-    }
-    return " AND ".join(clauses), params
+    clauses: list[str] = []
+    params: dict[str, Any] = {}
+    if args.source is not None:
+        clauses.append("source = :source")
+        params["source"] = args.source
+    if args.prompt_version is not None:
+        clauses.append("prompt_version = :prompt_version")
+        params["prompt_version"] = args.prompt_version
+    if args.since is not None:
+        clauses.append("created_at >= CAST(:since AS TIMESTAMPTZ)")
+        params["since"] = args.since
+    if args.until is not None:
+        clauses.append("created_at < CAST(:until AS TIMESTAMPTZ)")
+        params["until"] = args.until
+    return (" AND ".join(clauses) if clauses else "TRUE"), params
 
 
 # ─── eval split (id 해시) ────────────────────────────────