diff --git a/server-rs/crates/module-runtime/src/membership/upgrade.rs b/server-rs/crates/module-runtime/src/membership/upgrade.rs
index 317b410d1..29e9f18b8 100644
--- a/server-rs/crates/module-runtime/src/membership/upgrade.rs
+++ b/server-rs/crates/module-runtime/src/membership/upgrade.rs
@@ -200,7 +200,11 @@ pub fn quote_runtime_profile_membership_upgrade(
 }
 
 /// 向上取整的整数除法（金额取整到分）。
+///
+/// 分母是 `MONTHS_PER_YEAR * REMAINING_RATIO_PPM` 这类编译期常量，恒不为 0；
+/// 零分母属程序员错误，`debug_assert` 让它在测试里立刻暴露，而不是被静默算成 0 元。
 fn ceil_div(numerator: u128, denominator: u128) -> u64 {
+    debug_assert!(denominator != 0, "ceil_div 的分母不能为 0");
     if denominator == 0 {
         return 0;
     }