diff --git a/code/datums/material_container.dm b/code/datums/material_container.dm
index 6870c3d303b..cf8d3100b05 100644
--- a/code/datums/material_container.dm
+++ b/code/datums/material_container.dm
@@ -60,9 +60,14 @@
 	return 0
 
 /datum/material_container/proc/insert_stack(obj/item/stack/S, amt = 0)
-	if(!amt)
+	if(amt <= 0)
+		return 0
+	if(amt > S.amount)
 		amt = S.amount
 	var/material_amt = get_item_material_amount(S)
+	if(!material_amt)
+		return 0
+
 	amt = min(amt, round(((max_amount - total_amount) / material_amt)))
 	if(!amt)
 		return 0
diff --git a/code/modules/research/protolathe.dm b/code/modules/research/protolathe.dm
index 3d0c23ddb44..d4348ffb505 100644
--- a/code/modules/research/protolathe.dm
+++ b/code/modules/research/protolathe.dm
@@ -123,10 +123,12 @@ Note: Must be placed west/left of and R&D console to function.
 		return
 	if (stat)
 		return 1
-	if(istype(O,/obj/item/stack/sheet))
-		if(!materials.has_space( materials.get_item_material_amount(O) ))
-			user << "<span class='warning'>The [src.name]'s material bin is full. Please remove material before adding more.</span>"
-			return 1
+	if(!istype(O,/obj/item/stack/sheet))
+		return 1
+
+	if(!materials.has_space( materials.get_item_material_amount(O) ))
+		user << "<span class='warning'>The [src.name]'s material bin is full! Please remove material before adding more.</span>"
+		return 1
 
 	var/obj/item/stack/sheet/stack = O
 	var/amount = round(input("How many sheets do you want to add?") as num)//No decimals
@@ -134,14 +136,14 @@ Note: Must be placed west/left of and R&D console to function.
 		return
 	var/amount_inserted = materials.insert_stack(O,amount)
 	if(!amount_inserted)
-		user << "<span class='warning'>You could not insert [O], it has no usable materials.</span>"
 		return 1
 	else
 		busy = 1
 		use_power(max(1000, (MINERAL_MATERIAL_AMOUNT*amount_inserted/10)))
 		user << "<span class='notice'>You add [amount_inserted] sheets to the [src.name].</span>"
-		overlays += "protolathe_[stack.name]"
+		var/stackname = stack.name
+		src.overlays += "protolathe_[stackname]"
 		sleep(10)
-		overlays -= "protolathe_[stack.name]"
+		src.overlays -= "protolathe_[stackname]"
 		busy = 0
 	updateUsrDialog()
\ No newline at end of file