diff --git a/crates/engine/src/ai_support/combat_withdrawal.rs b/crates/engine/src/ai_support/combat_withdrawal.rs
index ddf1bf8587..7956975b76 100644
--- a/crates/engine/src/ai_support/combat_withdrawal.rs
+++ b/crates/engine/src/ai_support/combat_withdrawal.rs
@@ -188,7 +188,10 @@ fn is_exact_combat_withdrawal_path(ability: &ResolvedAbility) -> bool {
 fn single_member(
     members: &[crate::types::identifiers::ObjectId],
 ) -> Option<crate::types::identifiers::ObjectId> {
-    (members.len() == 1).then_some(members[0])
+    let [member] = members else {
+        return None;
+    };
+    Some(*member)
 }
 
 #[cfg(test)]
@@ -298,6 +301,15 @@ mod tests {
         )
     }
 
+    #[test]
+    fn single_member_rejects_empty_and_multi_member_slices() {
+        let member = ObjectId(1);
+
+        assert_eq!(single_member(&[]), None);
+        assert_eq!(single_member(&[member]), Some(member));
+        assert_eq!(single_member(&[member, ObjectId(2)]), None);
+    }
+
     #[test]
     fn direct_target_reports_exact_attacker_fact_without_mutating_state() {
         let (mut state, source, attacker, blocker) = combat_state();