diff --git a/static/index.js b/static/index.js
index 1bfd103..09acbcb 100644
--- a/static/index.js
+++ b/static/index.js
@@ -18,6 +18,7 @@ function load_teachers(id) {
   fetch(`/api/professori?id=${id}`)
     .then((response) => response.json())
     .then((data) => {
+      sessionStorage.setItem("teachers", JSON.stringify(data));
       let i = 0;
       data.forEach((el) => {
         const select = document.getElementById("teachers");
@@ -151,8 +152,13 @@ function load_major() {
 }
 
 function select_teacher() {
+  let teacher = document.getElementById("teacher").value;
+  let teachers = JSON.parse(sessionStorage.getItem("teachers"));
+  if (!teachers.includes(teacher)) {
+    return false;
+  }
   Cookies.set("type", "teacher");
-  Cookies.set("teacher", document.getElementById("teacher").value);
+  Cookies.set("teacher", teacher);
 }
 
 function select_class() {