diff --git a/app/services/courses_service.rb b/app/services/courses_service.rb
index 6e2c84e65..dee7af56d 100644
--- a/app/services/courses_service.rb
+++ b/app/services/courses_service.rb
@@ -56,7 +56,7 @@ class CoursesService
     else
       c = Course.find(course)
     end
-    if !(current_user.admin? || c.is_public == 1 || (c.is_public == 0 && current_user.member_of_course?(c)))
+    if current_user.nil? || !(current_user.admin? || c.is_public == 1 || (c.is_public == 0 && current_user.member_of_course?(c)))
       raise '403'
     end
     @teachers= searchTeacherAndAssistant(c)