diff --git a/frontend/src/components/atoms/BlockContent/BlockContent.tsx b/frontend/src/components/atoms/BlockContent/BlockContent.tsx
index ff3b6b4..95a5c5a 100644
--- a/frontend/src/components/atoms/BlockContent/BlockContent.tsx
+++ b/frontend/src/components/atoms/BlockContent/BlockContent.tsx
@@ -88,17 +88,19 @@ function BlockContent(blockDTO: Block) {
     if (focusId === blockDTO.id) contentEditableRef.current.focus();
   }, [focusId]);
 
+  const upperBlocks: Array<Block> = prevSiblings?.reverse();
+
   const isUpperBlockEqualToNumberList = (): boolean => {
-    if (prevSiblings.length) {
-      return prevSiblings[0].type === BlockType.NUMBERED_LIST;
+    if (upperBlocks.length) {
+      return upperBlocks[0].type === BlockType.NUMBERED_LIST;
     }
     return false;
   };
 
   const cntOfUpperNumberListBlock = (): number => {
     let cnt = 0;
-    if (prevSiblings) {
-      for (const upperblock of prevSiblings) {
+    if (upperBlocks) {
+      for (const upperblock of upperBlocks) {
         if (upperblock.type !== BlockType.NUMBERED_LIST) break;
         cnt += 1;
       }
diff --git a/frontend/src/hooks/useFamily.tsx b/frontend/src/hooks/useFamily.tsx
index 37ddab0..2565777 100644
--- a/frontend/src/hooks/useFamily.tsx
+++ b/frontend/src/hooks/useFamily.tsx
@@ -27,7 +27,7 @@ const useFamily = (blockId: string): [BlockFamily, FamilyFunc] => {
   );
   const prevSibling = siblings?.[blockIndex - 1];
   const nextSibling = siblings?.[blockIndex + 1];
-  const prevSiblings = siblings?.slice(0, blockIndex).reverse();
+  const prevSiblings = siblings?.slice(0, blockIndex);
   const nextSiblings = siblings?.slice(blockIndex);
 
   const findLastDescendant = (targetBlock: Block) => {