diff --git a/src/pages/thread/CommentSection.js b/src/pages/thread/CommentSection.js
index 81a4689..dc975e8 100644
--- a/src/pages/thread/CommentSection.js
+++ b/src/pages/thread/CommentSection.js
@@ -7,18 +7,18 @@ import {
 } from '../../utils'
 
 const arrayToLookup = (commentList, removed, deleted) => {
-  const lookup = {}
+  const lookup = new Map()
 
   commentList.forEach(comment => {
     comment.replies = []
 
-    if (removed.includes(comment.id)) {
+    if (removed.has(comment.id)) {
       comment.removed = true
-    } else if (deleted.includes(comment.id)) {
+    } else if (deleted.has(comment.id)) {
       comment.deleted = true
     }
 
-    lookup[comment.id] = comment
+    lookup.set(comment.id, comment)
   })
 
   return lookup
@@ -28,25 +28,23 @@ const unflatten = (comments, root, removed, deleted) => {
   const lookup = arrayToLookup(comments, removed, deleted)
   const commentTree = []
 
-  Object.keys(lookup).forEach(commentID => {
-    const comment = lookup[commentID]
+  lookup.forEach(comment => {
     const parentID = comment.parent_id
+    let parentComment
 
     if (parentID === root) {
       commentTree.push(comment)
+    } else if ((parentComment = lookup.get(parentID)) !== undefined) {
+      parentComment.replies.push(comment)
     } else {
-      if (lookup[parentID] === undefined) {
-        console.error('MISSING PARENT ID:', parentID, 'for comment', comment)
-        return
-      }
-
-      lookup[parentID].replies.push(comment)
+      console.error('MISSING PARENT ID:', parentID, 'for comment', comment)
     }
   })
 
-  if (lookup[root] !== undefined) {
-    lookup[root].replies = commentTree
-    return [lookup[root]]
+  let rootComment
+  if ((rootComment = lookup.get(root)) !== undefined) {
+    rootComment.replies = commentTree
+    return rootComment
   }
 
   return commentTree
diff --git a/src/pages/thread/index.js b/src/pages/thread/index.js
index 70dfbd0..870b5ec 100644
--- a/src/pages/thread/index.js
+++ b/src/pages/thread/index.js
@@ -19,8 +19,8 @@ class Thread extends React.Component {
   state = {
     post: {},
     pushshiftComments: [],
-    removed: [],
-    deleted: [],
+    removed: new Set(),
+    deleted: new Set(),
     loadingComments: true
   }
 
@@ -73,8 +73,8 @@ class Thread extends React.Component {
         return getRedditComments(ids)
           .then(redditComments => {
             console.log(`Reddit: ${redditComments.length} comments`)
-            const removed = []
-            const deleted = []
+            const removed = new Set()
+            const deleted = new Set()
 
             redditComments.forEach(comment => {
               const pushshiftComment = pushshiftCommentLookup.get(comment.id)
@@ -90,9 +90,9 @@ class Thread extends React.Component {
 
               // Check what is removed / deleted according to reddit
               if (isRemoved(comment.body)) {
-                removed.push(comment.id)
+                removed.add(comment.id)
               } else if (isDeleted(comment.body)) {
-                deleted.push(comment.id)
+                deleted.add(comment.id)
               }
             })
 
@@ -124,8 +124,8 @@ class Thread extends React.Component {
           <React.Fragment>
             <CommentInfo
               total={this.state.pushshiftComments.length}
-              removed={this.state.removed.length}
-              deleted={this.state.deleted.length}
+              removed={this.state.removed.size}
+              deleted={this.state.deleted.size}
             />
             <SortBy />
             {isSingleComment &&