diff --git a/server-rs/crates/module-runtime/src/membership/upgrade.rs b/server-rs/crates/module-runtime/src/membership/upgrade.rs
index 29e9f18b8..df71b8e1c 100644
--- a/server-rs/crates/module-runtime/src/membership/upgrade.rs
+++ b/server-rs/crates/module-runtime/src/membership/upgrade.rs
@@ -127,12 +127,15 @@ pub fn check_runtime_profile_membership_upgrade_allowed(
 /// 总期数不在入参里，而是由目标周期类型推导（`cycle_kind.cycle_count()`），所以「期号越界」
 /// 相对该推导值判断，`cycle_count` 与周期类型天然对齐。`now` 只校验下界——已过期报价按
 /// 「剩余比例为 0」返回，属既有契约。
+///
+/// 账期窗口要求严格递增（`cycle_started_at < cycle_resets_at`）：零时长窗口没有有效分母，
+/// 按非法入参拒绝，而不是让它退化成「剩余比例为 0」。
 fn validate_runtime_profile_membership_upgrade_quote_input(
     input: &RuntimeProfileMembershipUpgradeQuoteInput,
 ) -> Result<(), RuntimeProfileMembershipUpgradeRejection> {
     let cycle_count = input.target.cycle_kind.cycle_count();
     let cycle_index_out_of_range = input.cycle_index == 0 || input.cycle_index > cycle_count;
-    let window_out_of_order = input.cycle_resets_at_micros < input.cycle_started_at_micros;
+    let window_out_of_order = input.cycle_resets_at_micros <= input.cycle_started_at_micros;
     let now_before_window = input.now_micros < input.cycle_started_at_micros;
     if cycle_index_out_of_range || window_out_of_order || now_before_window {
         return Err(RuntimeProfileMembershipUpgradeRejection::InvalidQuoteInput);