diff --git a/protocol/tagtinker_proto.c b/protocol/tagtinker_proto.c
index e463268..5daa110 100644
--- a/protocol/tagtinker_proto.c
+++ b/protocol/tagtinker_proto.c
@@ -286,8 +286,8 @@ void tagtinker_free_image_payload(TagTinkerImagePayload* payload) {
 
 bool tagtinker_is_barcode_valid(const char* barcode) {
     if(!barcode || strlen(barcode) != 17) return false;
-    int cs = 0; for(int i = 0; i < 16; i++) cs += (int)(barcode[i] - '0');
-    return ((cs % 10) == (barcode[16] - '0'));
+    int cs = 0; for(int i = 0; i < 17; i++) cs += (int)(barcode[i] - '0');
+    return (cs % 10) == 0;
 }
 
 size_t tagtinker_make_addressed_frame(uint8_t* buf, const uint8_t plid[4], const uint8_t* payload, size_t len) {