diff --git a/server-rs/crates/module-runtime/src/civil_calendar.rs b/server-rs/crates/module-runtime/src/civil_calendar.rs
index 60c0a4ec8..bc6cec172 100644
--- a/server-rs/crates/module-runtime/src/civil_calendar.rs
+++ b/server-rs/crates/module-runtime/src/civil_calendar.rs
@@ -54,7 +54,7 @@ pub fn civil_from_days(date_key: i64) -> (i32, u8, u8) {
 /// ISO 星期：周一 = 1，周日 = 7。
 pub fn weekday_from_date_key(date_key: i64) -> u8 {
     // 中文注释：1970-01-01 是周四；这里返回 ISO weekday，周一=1，周日=7。
-    (date_key + 3).rem_euclid(7) as u8 + 1
+    (date_key.rem_euclid(7) + 3).rem_euclid(7) as u8 + 1
 }
 
 #[cfg(test)]