diff --git a/src/tests/speedtest.ts b/src/tests/speedtest.ts
index aefb2a1..0ed4372 100644
--- a/src/tests/speedtest.ts
+++ b/src/tests/speedtest.ts
@@ -56,11 +56,11 @@ function idToEan13(id): string {
     while (id.length < 12) { id = '0' + id; }
 
     let total = 0;
-    this.id.split('').forEach((letter, index) => {
+    id.split('').forEach((letter, index) => {
         total += parseInt(letter, 10) * multiply[index % 2];
     });
     const checkSum = (Math.ceil(total / 10) * 10) - total;
-    return this.id + checkSum.toString();
+    return id + checkSum.toString();
 }
 
 async function postContracts(runners: Runner[]): Promise<Measurement> {