diff --git a/crates/oxide_builtins/src/temporal/duration.rs b/crates/oxide_builtins/src/temporal/duration.rs
index 15fac9a8..47d95efb 100644
--- a/crates/oxide_builtins/src/temporal/duration.rs
+++ b/crates/oxide_builtins/src/temporal/duration.rs
@@ -410,7 +410,8 @@ fn duration_relative_to_date<H: VmHost>(vm: &mut H, relative_raw: JsValue) -> Re
     // calendar 经宽松版接受：白名单/ISO 串（非法 RangeError）、Temporal 实例读日历槽、其余 TypeError。
     let calendar_raw = temporal_option_value(vm, obj, relative_raw, "calendar")?;
     let calendar = temporal_calendar_id(vm, calendar_raw)?;
-    let non_iso_calendar = calendar.as_deref() != Some("iso8601");
+    // calendar 未提供（undefined）时默认 iso8601，era/eraYear 不读；仅具体非 iso8601 日历才读。
+    let non_iso_calendar = calendar.as_deref().map(|c| c != "iso8601").unwrap_or(false);
 
     let day_raw = temporal_option_value(vm, obj, relative_raw, "day")?;
     let day = bag_number_field(vm, day_raw)?;
diff --git a/crates/oxide_vm/tests/builtins_temporal_tests.rs b/crates/oxide_vm/tests/builtins_temporal_tests.rs
index ad7f660b..3c9d749e 100644
--- a/crates/oxide_vm/tests/builtins_temporal_tests.rs
+++ b/crates/oxide_vm/tests/builtins_temporal_tests.rs
@@ -4004,6 +4004,52 @@ fn relativeto_bag_era_merge() {
     assert_eq!(str_val(&vm, r), "ok|ok|ok|ok|RangeError|RangeError|TypeError|TypeError");
 }
 
+#[test]
+fn relativeto_bag_era_gate_calendar_default() {
+    let mut vm = Vm::new();
+    // era/eraYear 读取门：calendar 未提供（默认 iso8601）时 era/eraYear 不读不合并，
+    // 缺 year 按 iso8601 语义抛 TypeError「year is required」；同袋带 year 时 era/eraYear
+    // 被忽略取 year；calendar 为具体非 iso8601（gregory）时读取并合并。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const kind = (fn) => { try { fn(); return 'ok'; } catch (e) { return e.constructor.name + ':' + e.message; } };
+           const d = new Temporal.Duration(1, 0, 0, 0, 24);
+           const round = (rel) => d.round({ largestUnit: 'years', relativeTo: rel });
+           return [
+             kind(() => round({ month: 5, day: 2, era: 'ad', eraYear: 2020 })),
+             kind(() => round({ year: 2020, month: 5, day: 2, era: 'ad', eraYear: 2021 })),
+             kind(() => round({ month: 5, day: 2, calendar: 'gregory', era: 'ad', eraYear: 2020 })),
+             kind(() => round({ year: 2020, month: 5, day: 2, calendar: 'gregory', era: 'ad', eraYear: 2020 })),
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(str_val(&vm, r), "TypeError:year is required|ok|ok|ok");
+}
+
+#[test]
+fn relativeto_bag_read_order_no_calendar_skips_era() {
+    let mut vm = Vm::new();
+    // 读序门：calendar 未提供（默认 iso8601）时 era/eraYear 不进读序，
+    // 与 iso8601 袋读序一致；若误读 era/eraYear，序中会出现 era,eraYear。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const order = [];
+           const values = { day: 2, era: 'ad', eraYear: 2020, month: 5, year: 2020 };
+           const rel = {};
+           for (const k of Object.keys(values)) {
+             Object.defineProperty(rel, k, { get() { order.push(k); return values[k]; }, configurable: true });
+           }
+           Temporal.Duration.compare(new Temporal.Duration(1), new Temporal.Duration(0), { relativeTo: rel });
+           return order.join(',');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(str_val(&vm, r), "day,month,year");
+}
+
 #[test]
 fn relativeto_bag_read_order_calendar_first_dictionary() {
     let mut vm = Vm::new();