diff --git a/api/views.py b/api/views.py
index 1f6d1256..80d77d7b 100644
--- a/api/views.py
+++ b/api/views.py
@@ -783,7 +783,9 @@ def import_activities(request):
         )
         res["count"] = len(res["users"])
     except (ImportException, UnicodeDecodeError) as e:
-        res["error"] = "".join(traceback.TracebackException.from_exception(e).format())
+        # msg = traceback.TracebackException.from_exception(e).format()
+        msg = e.args[0]
+        res["error"] = msg
     except BaseException:
         res["error"] = traceback.format_exc()
 
diff --git a/common/bulk_import.py b/common/bulk_import.py
index 76c1d119..dd470e64 100644
--- a/common/bulk_import.py
+++ b/common/bulk_import.py
@@ -78,8 +78,12 @@ def run(
                         )
             else:
                 # We assign all activities without teacher in INBUS to the one selected by importing user
-                teacher_username = activities_to_teacher[ca.concreteActivityId]
-                teacher = User.objects.get(username=teacher_username)
+                try:
+                    teacher_username = activities_to_teacher[ca.concreteActivityId]
+                    teacher = User.objects.get(username=teacher_username)
+                except KeyError:
+                    msg = f"There's no assigned teacher to activity {ca.code()}. Please, make sure you selected one."
+                    raise ImportException(msg)
 
             if not is_teacher(teacher):
                 teachers_group = Group.objects.get_by_natural_key("teachers")
diff --git a/frontend/src/Teacher/InbusImport.vue b/frontend/src/Teacher/InbusImport.vue
index f690f813..9bff1e82 100644
--- a/frontend/src/Teacher/InbusImport.vue
+++ b/frontend/src/Teacher/InbusImport.vue
@@ -41,6 +41,13 @@ interface Teacher {
   last_name: string;
 }
 
+interface ImportRequest {
+  semester_id: number;
+  subject_abbr: string;
+  activities: number[];
+  activities_to_teacher: { [key: number]: string };
+}
+
 const busy = ref<boolean>(false);
 
 const semesters = await loadSemesters();
@@ -175,15 +182,76 @@ async function loadTeachers(): Promise<Teacher[]> {
   return teachers;
 }
 
+function classesWithoutTeacher() {
+  const classes_without_teacher: number[] = [];
+  for (const clazz of subject_inbus_schedule.value) {
+    if (!clazz.teacherFullNames) {
+      classes_without_teacher.push(clazz.concreteActivityId);
+    }
+  }
+
+  return classes_without_teacher;
+}
+
+function isRequestValid(req) {
+  const classes_without_teacher = classesWithoutTeacher();
+
+  for (const activity of req.activities) {
+    if (classes_without_teacher.includes(activity)) {
+      if (!req.activities_to_teacher.hasOwnProperty(activity)) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+function getCorrespondingActivityRepr(activity_id: number) {
+  for (const ca of subject_inbus_schedule.value) {
+    if (ca.concreteActivityId === activity_id) {
+      return `${ca.educationTypeAbbrev}/${ca.order}, ${ca.subjectVersionCompleteCode}`;
+    }
+  }
+}
+
+function classesWithoutSelectedTeacher(req: ImportRequest) {
+  const classes_without_selected_teacher: string[] = [];
+  const classes_without_teacher = classesWithoutTeacher();
+  //console.log('classes_without_teacher', classes_without_teacher);
+
+  for (const activity_id of req.activities) {
+    if (classes_without_teacher.includes(activity_id)) {
+      if (!req.activities_to_teacher.hasOwnProperty(activity_id)) {
+        classes_without_selected_teacher.push(getCorrespondingActivityRepr(activity_id));
+      }
+    }
+  }
+
+  return classes_without_selected_teacher;
+}
+
 async function importActivities() {
   busy.value = true;
-  const req = {
+  const req: ImportRequest = {
     semester_id: semester.value,
     subject_abbr: subject_kelvin_selected.value,
     activities: classes_to_import.value,
     activities_to_teacher: activities_to_teacher_selected.value
   };
 
+  if (!isRequestValid(req)) {
+    const classes_without_selected_teacher = classesWithoutSelectedTeacher(req);
+    const err_msg =
+      classes_without_selected_teacher.length > 1
+        ? `Selected classes to import (${classes_without_selected_teacher.join(', ')}) don't have assigned teacher. Please, select ones.`
+        : `Selected class to import (${classes_without_selected_teacher}) doesn't have assigned teacher. Please, select one.`;
+    result.value = { users: [], count: 0, error: err_msg };
+    busy.value = false;
+
+    return;
+  }
+
   const res = await fetch('/api/import/activities', {
     method: 'POST',
     headers: {
@@ -254,6 +322,7 @@ function onTeacherSelected(event) {
           <span v-if="ca.teacherFullNames">{{ ca.teacherFullNames }}</span>
           <span v-else>
             <select @change="onTeacherSelected">
+              <option value="">Select teacher</option>
               <option
                 v-for="teacher in teachers"
                 :key="teacher.username"