diff --git a/web/src/components/MemoEditor/index.tsx b/web/src/components/MemoEditor/index.tsx
index 0cfb586a..4264ce4f 100644
--- a/web/src/components/MemoEditor/index.tsx
+++ b/web/src/components/MemoEditor/index.tsx
@@ -388,7 +388,7 @@ const MemoEditor = (props: Props) => {
 
   return (
     <div
-      className={`${className} memo-editor-container ${state.fullscreen ? "fullscreen" : ""}`}
+      className={`${className ?? ""} memo-editor-container ${state.fullscreen ? "fullscreen" : ""}`}
       tabIndex={0}
       onKeyDown={handleKeyDown}
       onDrop={handleDropEvent}