diff --git a/api/views/default.py b/api/views/default.py
index 21d172e0a..776a9fd25 100644
--- a/api/views/default.py
+++ b/api/views/default.py
@@ -392,7 +392,7 @@ def add_student_to_class(request, class_id):
     username = data["username"]
 
     errors = []
-
+    already_assigned = []
     for username in data["username"]:
         username = username.strip().upper()
         user = None
@@ -406,6 +406,10 @@ def add_student_to_class(request, class_id):
                 user.save()
 
         if user:
+            if Class.objects.filter(subject=clazz.subject, students=user).exists():
+                already_assigned.append(username)
+                errors.append(username)
+                continue
             clazz.students.add(user)
         else:
             errors.append(username)
@@ -414,6 +418,7 @@ def add_student_to_class(request, class_id):
         {
             "success": not errors,
             "not_found": errors,
+            "already_assigned": already_assigned,
         }
     )
 
diff --git a/common/bulk_import.py b/common/bulk_import.py
index dd470e648..f5a409f83 100644
--- a/common/bulk_import.py
+++ b/common/bulk_import.py
@@ -22,6 +22,7 @@ class ImportResult:
     firstname: str
     lastname: str
     created: bool
+    already_assigned: bool
 
 
 def run(
@@ -103,6 +104,7 @@ def run(
             firstname, lastname = student.firstName, student.secondName
 
             created = False
+            already_assigned = False
 
             student_user = None
             try:
@@ -111,6 +113,9 @@ def run(
                 student_user = user_from_login(login)
                 created = True
 
-            class_in_db[c].students.add(student_user)
+            if Class.objects.filter(subject=class_in_db[c].subject, students=user).exists():
+                already_assigned = True
+            else:
+                class_in_db[c].students.add(student_user)
 
-            yield ImportResult(login, firstname, lastname, created)
+            yield ImportResult(login, firstname, lastname, created, already_assigned)
diff --git a/frontend/src/AddStudentsToClass.svelte b/frontend/src/AddStudentsToClass.svelte
index 0e827a09b..8e26e61d9 100644
--- a/frontend/src/AddStudentsToClass.svelte
+++ b/frontend/src/AddStudentsToClass.svelte
@@ -42,8 +42,11 @@ async function addStudents() {
     let res = await req.json();
     if (res) {
       if (res['not_found'].length) {
-        addStudentError = 'Not found users left in textarea.';
-        textarea = res['not_found'].join('\n');
+        addStudentError =
+          'Not found users left in textarea. Already assigned students are separated by a newline';
+        textarea = res['not_found'].filter((x) => !res['already_assigned'].includes(x)).join('\n');
+        textarea += '\n\n';
+        textarea += res['already_assigned'].join('\n');
         dispatch('update');
       } else if (res['success'] === true) {
         textarea = '';
diff --git a/frontend/src/Teacher/InbusImport.vue b/frontend/src/Teacher/InbusImport.vue
index 4a6450d5c..ff2544de3 100644
--- a/frontend/src/Teacher/InbusImport.vue
+++ b/frontend/src/Teacher/InbusImport.vue
@@ -28,6 +28,7 @@ interface ImportResult {
   firstname: string;
   lastname: string;
   created: boolean;
+  already_assigned: boolean;
 }
 
 interface Result {
@@ -374,6 +375,7 @@ function onTeacherSelected(event) {
               <th>First name</th>
               <th>Last name</th>
               <th>User created</th>
+              <th>Already assigned</th>
             </tr>
           </thead>
           <tbody>
@@ -382,6 +384,7 @@ function onTeacherSelected(event) {
               <td>{{ item.firstname }}</td>
               <td>{{ item.lastname }}</td>
               <td>{{ item.created }}</td>
+              <td>{{ item.already_assigned }}</td>
             </tr>
           </tbody>
         </table>