diff --git a/code/datums/material_container.dm b/code/datums/material_container.dm
index cf8d3100b05..8f84812e49e 100644
--- a/code/datums/material_container.dm
+++ b/code/datums/material_container.dm
@@ -80,7 +80,8 @@
 	if(!I)
 		return 0
 	if(istype(I,/obj/item/stack))
-		return insert_stack(I)
+		var/obj/item/stack/S = I
+		return insert_stack(I, S.amount)
 
 	var/material_amount = get_item_material_amount(I)
 	if(!material_amount || !has_space(material_amount))