diff --git a/utils/post_utils.jsx b/utils/post_utils.jsx
index a9d152652027..50a29dc4b942 100644
--- a/utils/post_utils.jsx
+++ b/utils/post_utils.jsx
@@ -225,18 +225,23 @@ export function isErrorInvalidSlashCommand(error) {
     return false;
 }
 
+function isIdNotPost(postId) {
+    return (
+        PostListUtils.isStartOfNewMessages(postId) ||
+        PostListUtils.isDateLine(postId) ||
+        postId === PostListRowListIds.CHANNEL_INTRO_MESSAGE ||
+        postId === PostListRowListIds.MORE_MESSAGES_LOADER ||
+        postId === PostListRowListIds.MANUAL_TRIGGER_LOAD_MESSAGES
+    );
+}
+
 // getLastPostId returns the most recent post ID in the given list of post IDs. This function is copied from
 // mattermost-redux, except it also includes additional special IDs that are only used in the web app.
 export function getLastPostId(postIds) {
     for (let i = postIds.length - 1; i >= 0; i--) {
         const item = postIds[i];
 
-        if (
-            PostListUtils.isStartOfNewMessages(item) ||
-            PostListUtils.isDateLine(item) ||
-            item === PostListRowListIds.CHANNEL_INTRO_MESSAGE ||
-            item === PostListRowListIds.MORE_MESSAGES_LOADER
-        ) {
+        if (isIdNotPost(item)) {
             // This is not a post at all
             continue;
         }
diff --git a/utils/post_utils.test.jsx b/utils/post_utils.test.jsx
index 06a76d415f9f..278ba0d0712a 100644
--- a/utils/post_utils.test.jsx
+++ b/utils/post_utils.test.jsx
@@ -4,6 +4,7 @@
 import assert from 'assert';
 
 import * as PostUtils from 'utils/post_utils.jsx';
+import {PostListRowListIds} from 'utils/constants.jsx';
 
 describe('PostUtils.containsAtChannel', () => {
     test('should return correct @all (same for @channel)', () => {
@@ -524,3 +525,30 @@ describe('PostUtils.postMessageOnKeyPress', () => {
         });
     }
 });
+
+describe('PostUtils.getLastPostId', () => {
+    test('Should not return MANUAL_TRIGGER_LOAD_MESSAGES', () => {
+        const postId = PostUtils.getLastPostId(['postId1', 'postId2', PostListRowListIds.MANUAL_TRIGGER_LOAD_MESSAGES]);
+        assert.equal(postId, 'postId2');
+    });
+
+    test('Should not return MORE_MESSAGES_LOADER', () => {
+        const postId = PostUtils.getLastPostId(['postId1', 'postId2', PostListRowListIds.MORE_MESSAGES_LOADER]);
+        assert.equal(postId, 'postId2');
+    });
+
+    test('Should not return CHANNEL_INTRO_MESSAGE', () => {
+        const postId = PostUtils.getLastPostId(['postId1', 'postId2', PostListRowListIds.CHANNEL_INTRO_MESSAGE]);
+        assert.equal(postId, 'postId2');
+    });
+
+    test('Should not return dateline', () => {
+        const postId = PostUtils.getLastPostId(['postId1', 'postId2', 'date-1558290600000']);
+        assert.equal(postId, 'postId2');
+    });
+
+    test('Should not return START_OF_NEW_MESSAGES', () => {
+        const postId = PostUtils.getLastPostId(['postId1', 'postId2', PostListRowListIds.START_OF_NEW_MESSAGES]);
+        assert.equal(postId, 'postId2');
+    });
+});