diff --git a/backend/src/main.ts b/backend/src/main.ts
index cd87e63..be1538a 100644
--- a/backend/src/main.ts
+++ b/backend/src/main.ts
@@ -120,9 +120,9 @@ const password = encodeURIComponent(env["LATEINICUS_USER_PW"]);
         const { username, password, classId } = req.body;
 
         // Check if the registration is open for the class Id
-        // NOTE: Thiis to prevent people from spamming the database
+        // NOTE: This to prevent people from spamming the database
         const classes = env["LATEINICUS_CLASSES"].split(",");
-        if (classes.indexOf(classId) !== -1) {
+        if (classes.indexOf(classId) === -1) {
             res.send({
                 error: "403",
                 data: {