diff --git a/mailbox.lua b/mailbox.lua
index a0f0528..dbfd09e 100644
--- a/mailbox.lua
+++ b/mailbox.lua
@@ -2,11 +2,13 @@ local mailbox = {}
 screwdriver = screwdriver or {}
 
 local function img_col(stack)
-	if not stack then return "" end
-	if stack.inventory_image ~= "" then
-		return stack.inventory_image:match("(.*)%.png")..".png"
+	local def = minetest.registered_items[stack]
+	if not def then return "" end
+
+	if def.inventory_image ~= "" then
+		return def.inventory_image:match("(.*)%.png")..".png"
 	else
-		return stack.tiles[1]:match("(.*)%.png")..".png"
+		return def.tiles[1]:match("(.*)%.png")..".png"
 	end
 end
 
@@ -23,7 +25,9 @@ function mailbox:formspec(pos, owner, num)
 				local stack_count = meta:get_string("stack"..i):match("%s(%d+)") or 1
 
 				giver = giver.."#FFFF00,"..giver_name..","..i..",#FFFFFF,x "..stack_count..","
-				img = img..i.."="..img_col(minetest.registered_items[stack_name])..","
+				-- Hack to force using a 16px resolution for images in formspec's tablecolumn.
+				-- The engine doesn't scale them automatically yet.
+				img = img..i.."=mailbox_blank16.png^"..img_col(stack_name)..","
 			end
 		end
 
diff --git a/textures/mailbox_blank16.png b/textures/mailbox_blank16.png
new file mode 100644
index 0000000..849e622
Binary files /dev/null and b/textures/mailbox_blank16.png differ