diff --git a/code/modules/mob/living/simple_animal/simple_animal.dm b/code/modules/mob/living/simple_animal/simple_animal.dm
index 3bd82204b2b..d35370f68e7 100644
--- a/code/modules/mob/living/simple_animal/simple_animal.dm
+++ b/code/modules/mob/living/simple_animal/simple_animal.dm
@@ -574,5 +574,5 @@
 /mob/living/simple_animal/onTransitZ(old_z, new_z)
 	..()
 	if (AIStatus == AI_Z_OFF)
-		SSidlenpcpool[old_z] -= src
+		SSidlenpcpool.idle_mobs_by_zlevel[old_z] -= src
 		toggle_ai(initial(AIStatus))