diff --git a/rules.ini b/rules.ini
index 34338ddc33..8b753341e0 100644
--- a/rules.ini
+++ b/rules.ini
@@ -1228,7 +1228,7 @@ ROT=30
 
 ; big missile silo
 [MSLO]
-Prerequisite=stek
+Prerequisite=stek,atek
 Primary=none
 Strength=400
 Armor=heavy