diff --git a/src/pages/TimetablePage/components/CustomLecture/index.tsx b/src/pages/TimetablePage/components/CustomLecture/index.tsx
index 7602bdbf..bdfa2c66 100644
--- a/src/pages/TimetablePage/components/CustomLecture/index.tsx
+++ b/src/pages/TimetablePage/components/CustomLecture/index.tsx
@@ -121,7 +121,7 @@ function CustomLecture({ frameId }: { frameId: string | undefined }) {
     if (alreadySelectedLecture) {
       showToast(
         'error',
-        `${alreadySelectedLecture.class_title}(${alreadySelectedLecture.lecture_class}) 강의가 중복되어 추가할 수 없습니다.`,
+        `${alreadySelectedLecture.class_title} ${alreadySelectedLecture.lecture_class ? `(${alreadySelectedLecture.lecture_class})` : ''} 강의가 중복되어 추가할 수 없습니다.`,
       );
       return;
     }