diff --git a/code/game/machinery/doors/airlock.dm b/code/game/machinery/doors/airlock.dm
index c932c329dd..bec90e54fa 100644
--- a/code/game/machinery/doors/airlock.dm
+++ b/code/game/machinery/doors/airlock.dm
@@ -80,7 +80,7 @@
 	var/boltUp = 'sound/machines/boltsup.ogg'
 	var/boltDown = 'sound/machines/boltsdown.ogg'
 	var/noPower = 'sound/machines/doorclick.ogg'
-	var/previous_airlock //what airlock assembly mineral plating was applied to
+	var/previous_airlock = /obj/structure/door_assembly //what airlock assembly mineral plating was applied to
 	var/airlock_material = null //material of inner filling; if its an airlock with glass, this should be set to "glass"
 	var/overlays_file = 'icons/obj/doors/airlocks/station/overlays.dmi'
 	var/note_overlay_file = 'icons/obj/doors/airlocks/station/overlays.dmi' //Used for papers and photos pinned to the airlock