diff --git a/mods/lzr_laser/physics.lua b/mods/lzr_laser/physics.lua
index 8624dbf..93637cd 100644
--- a/mods/lzr_laser/physics.lua
+++ b/mods/lzr_laser/physics.lua
@@ -218,9 +218,9 @@ function lzr_laser.check_inventory_detectors(player, detector_placed)
 	local inv = player:get_inventory()
 	local count = 0
 	for i=1, inv:get_size("main") do
-		local item = inv:get_stack("main", i):get_name()
-		if minetest.get_item_group(item, "detector") ~= 0 then
-			count = count + 1
+		local item = inv:get_stack("main", i)
+		if minetest.get_item_group(item:get_name(), "detector") ~= 0 then
+			count = count + item:get_count()
 			if (detector_placed and count > 1) or (not detector_placed) then
 				return false
 			end