diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index f584117..3ac2077 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -36,7 +36,8 @@ export default (({ post, onSave }: Props) => {
       useState<string | null> (post.originalCreatedBefore)
   const [originalCreatedFrom, setOriginalCreatedFrom] =
       useState<string | null> (post.originalCreatedFrom)
-  const [parentPostIds, setParentPostIds] = useState (post.parentPosts!.map (p => p.id).join (' '))
+  const [parentPostIds, setParentPostIds] =
+      useState ((post.parentPosts ?? []).map (p => p.id).join (' '))
   const [tags, setTags] = useState<string> ('')
   const [title, setTitle] = useState (post.title)
 
diff --git a/frontend/src/components/PostList.tsx b/frontend/src/components/PostList.tsx
index 8bd6118..21a4410 100644
--- a/frontend/src/components/PostList.tsx
+++ b/frontend/src/components/PostList.tsx
@@ -42,8 +42,8 @@ export default (({ posts, onClick }: Props) => {
 		    layoutId={layoutId}
 		    className={cn ('w-full h-full overflow-hidden rounded-xl shadow',
 				   'transform-gpu will-change-transform',
-				   (post.childPosts ?? []).length > 0 && 'outline-4 border-green-500',
-				   (post.parentPosts ?? []).length > 0 && 'outline-4 border-yellow-500')}
+				   (post.childPosts ?? []).length > 0 && 'outline-4 outline-green-500',
+				   (post.parentPosts ?? []).length > 0 && 'ring-4 ring-yellow-500')}
 		    whileHover={{ scale: 1.02 }}
 		    onLayoutAnimationStart={() => {
 		      if (!(cardRef.current))
diff --git a/frontend/src/pages/posts/PostHistoryPage.tsx b/frontend/src/pages/posts/PostHistoryPage.tsx
index 825efe9..2977527 100644
--- a/frontend/src/pages/posts/PostHistoryPage.tsx
+++ b/frontend/src/pages/posts/PostHistoryPage.tsx
@@ -253,7 +253,7 @@ export default (() => {
 						  .filter (t => t.slice (0, 5) !== 'nico:')
 						  .join (' '),
 					    parent_post_ids:
-						change.parentPosts
+						(change.parentPosts ?? [])
 						.filter (p => p.type !== 'removed')
 						.map (p => p.id)
 						.join (' '),