diff --git a/server-rs/crates/module-runtime/src/civil_calendar.rs b/server-rs/crates/module-runtime/src/civil_calendar.rs
index bc6cec172..036bf1a2d 100644
--- a/server-rs/crates/module-runtime/src/civil_calendar.rs
+++ b/server-rs/crates/module-runtime/src/civil_calendar.rs
@@ -36,7 +36,7 @@ pub fn days_from_civil(year: i32, month: u8, day: u8) -> i64 {
 /// 1970-01-01 起的日序号 → 公历年月日。
 pub fn civil_from_days(date_key: i64) -> (i32, u8, u8) {
     // 中文注释：days_from_civil 的反向算法，避免依赖运行环境时区。
-    let z = date_key + 719_468;
+    let z = date_key.saturating_add(719_468);
     let era = z.div_euclid(146_097);
     let day_of_era = z - era * 146_097;
     let year_of_era = (day_of_era - day_of_era / 1_460 + day_of_era / 36_524