diff --git a/abrechenbarkeit.lua b/abrechenbarkeit.lua
index dee8b4d..3291224 100755
--- a/abrechenbarkeit.lua
+++ b/abrechenbarkeit.lua
@@ -746,6 +746,17 @@ local function r_products_post()
         if barcode == nil or barcode:match(matchers_global.barcode) == nil then
             return error_box("{+error.invalid_barcode}")
         end
+		local exists = false
+		for _, a_barcode in read_barcodes() do
+			if a_barcode == barcode then
+				exists = true
+			end
+		end
+
+		if exists then
+			return error_box("{+error.invalid_barcode}")
+		end
+
     	local barcodes = io.open("barcodes", "a+")
     	if barcodes == nil then
     		return error_box("{+error.open_barcodes}")