diff --git a/courses/serializers.py b/courses/serializers.py
index e4fe7ce..139b545 100644
--- a/courses/serializers.py
+++ b/courses/serializers.py
@@ -91,7 +91,7 @@ class CourseDetailSerializer(serializers.ModelSerializer):
 
     @staticmethod
     def get_teacher_emails(self):
-        return [get_user_model().objects.get(out_key=i).email for i in self.teacher_tokens]
+        return [i.email for i in get_user_model().objects.filter(out_key__in=self.teacher_tokens)]
 
     @staticmethod
     def get_level(self):