diff --git a/backend/src/main.ts b/backend/src/main.ts
index 288d34c..cd87e63 100644
--- a/backend/src/main.ts
+++ b/backend/src/main.ts
@@ -119,6 +119,19 @@ 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
+        const classes = env["LATEINICUS_CLASSES"].split(",");
+        if (classes.indexOf(classId) !== -1) {
+            res.send({
+                error: "403",
+                data: {
+                    msg: "Class does not exist",
+                },
+            });
+            return;
+        }
+
         // TODO: Check if the username is profane
         // if (profanityFilter.isProfane(username)) {
         //     res.send({