diff --git a/server-rs/crates/module-runtime/src/membership/upgrade.rs b/server-rs/crates/module-runtime/src/membership/upgrade.rs
index 051365bc5..64a9ae25a 100644
--- a/server-rs/crates/module-runtime/src/membership/upgrade.rs
+++ b/server-rs/crates/module-runtime/src/membership/upgrade.rs
@@ -182,15 +182,13 @@ pub fn quote_runtime_profile_membership_upgrade(
         input.now_micros,
     );
 
-    // 目录价格 / 每期泥点必须严格随 rank 递增；倒挂时宁可报错，也不算出 0 元升级。
-    let price_delta_cents = target
-        .price_cents
-        .checked_sub(current.price_cents)
-        .ok_or(RuntimeProfileMembershipUpgradeRejection::InvalidQuoteInput)?;
-    let points_delta = target
-        .period_points
-        .checked_sub(current.period_points)
-        .ok_or(RuntimeProfileMembershipUpgradeRejection::InvalidQuoteInput)?;
+    // 目录价格 / 每期泥点必须严格随 rank 递增；相等或倒挂都直接拒绝，
+    // 否则 checked_sub 会把「相等」算成 0 元升级 / 0 补点，违背目录不变量。
+    if target.price_cents <= current.price_cents || target.period_points <= current.period_points {
+        return Err(RuntimeProfileMembershipUpgradeRejection::InvalidQuoteInput);
+    }
+    let price_delta_cents = target.price_cents - current.price_cents;
+    let points_delta = target.period_points - current.period_points;
 
     let (amount_cents, granted_points_delta) = match target.cycle_kind {
         RuntimeProfileMembershipCycleKind::Monthly => (price_delta_cents, points_delta),
@@ -494,6 +492,19 @@ mod tests {
 
         target.price_cents = current.price_cents + 1;
         target.period_points = current.period_points - 1;
+        assert_eq!(
+            quote_runtime_profile_membership_upgrade(RuntimeProfileMembershipUpgradeQuoteInput {
+                current: current.clone(),
+                target: target.clone(),
+                ..base_input()
+            }),
+            Err(RuntimeProfileMembershipUpgradeRejection::InvalidQuoteInput)
+        );
+
+        // 中文注释：相等同样破坏「严格随 rank 递增」，必须拒绝；旧实现用 checked_sub
+        // 会把相等的价差 / 点差算成 0，从而产出 0 元升级 / 0 补点。
+        target.price_cents = current.price_cents;
+        target.period_points = current.period_points;
         assert_eq!(
             quote_runtime_profile_membership_upgrade(RuntimeProfileMembershipUpgradeQuoteInput {
                 current,