diff --git a/src/discussions/comments/CommentsView.jsx b/src/discussions/comments/CommentsView.jsx
index 77565562..9555a42b 100644
--- a/src/discussions/comments/CommentsView.jsx
+++ b/src/discussions/comments/CommentsView.jsx
@@ -18,6 +18,7 @@ import {
 import { useDispatchWithState } from '../../data/hooks';
 import { DiscussionContext } from '../common/context';
 import { useIsOnDesktop } from '../data/hooks';
+import { EmptyPage } from '../empty-posts';
 import { Post } from '../posts';
 import { selectThread } from '../posts/data/selectors';
 import { fetchThread, markThreadAsRead } from '../posts/data/thunks';
@@ -133,9 +134,9 @@ DiscussionCommentsView.propTypes = {
 };
 
 function CommentsView({ intl }) {
+  const [isLoading, submitDispatch] = useDispatchWithState();
   const { postId } = useParams();
   const thread = usePost(postId);
-  const dispatch = useDispatch();
   const history = useHistory();
   const location = useLocation();
   const isOnDesktop = useIsOnDesktop();
@@ -143,8 +144,16 @@ function CommentsView({ intl }) {
     courseId, learnerUsername, category, topicId, page, inContext,
   } = useContext(DiscussionContext);
 
+  useEffect(() => {
+    if (!thread) { submitDispatch(fetchThread(postId, courseId, true)); }
+  }, [postId]);
+
   if (!thread) {
-    dispatch(fetchThread(postId, true));
+    if (!isLoading) {
+      return (
+        <EmptyPage title={intl.formatMessage(messages.noThreadFound)} />
+      );
+    }
     return (
       <Spinner animation="border" variant="primary" data-testid="loading-indicator" />
     );
diff --git a/src/discussions/comments/CommentsView.test.jsx b/src/discussions/comments/CommentsView.test.jsx
index 52c01a81..d0389e0e 100644
--- a/src/discussions/comments/CommentsView.test.jsx
+++ b/src/discussions/comments/CommentsView.test.jsx
@@ -102,7 +102,7 @@ function renderComponent(postId) {
 }
 
 describe('CommentsView', () => {
-  beforeEach(async () => {
+  beforeEach(() => {
     initializeMockApp({
       authenticatedUser: {
         userId: 3,
@@ -147,7 +147,7 @@ describe('CommentsView', () => {
         )];
       });
 
-    await executeThunk(fetchThreads(courseId), store.dispatch, store.getState);
+    executeThunk(fetchThreads(courseId), store.dispatch, store.getState);
     mockAxiosReturnPagedComments();
     mockAxiosReturnPagedCommentsResponses();
   });
@@ -449,9 +449,9 @@ describe('CommentsView', () => {
   describe('for discussion thread', () => {
     const findLoadMoreCommentsButton = () => screen.findByTestId('load-more-comments');
 
-    it('shown spinner when post isn\'t loaded', async () => {
+    it('shown post not found when post id does not belong to course', async () => {
       renderComponent('unloaded-id');
-      expect(await screen.findByTestId('loading-indicator'))
+      expect(await screen.findByText('Thread not found', { exact: true }))
         .toBeInTheDocument();
     });
 
diff --git a/src/discussions/comments/comment/Comment.jsx b/src/discussions/comments/comment/Comment.jsx
index 2cdb6bc2..d6876339 100644
--- a/src/discussions/comments/comment/Comment.jsx
+++ b/src/discussions/comments/comment/Comment.jsx
@@ -1,4 +1,4 @@
-import React, { useEffect, useState } from 'react';
+import React, { useContext, useEffect, useState } from 'react';
 import PropTypes from 'prop-types';
 
 import classNames from 'classnames';
@@ -10,6 +10,7 @@ import { Button, useToggle } from '@edx/paragon';
 import HTMLLoader from '../../../components/HTMLLoader';
 import { ContentActions } from '../../../data/constants';
 import { AlertBanner, DeleteConfirmation, EndorsedAlertBanner } from '../../common';
+import { DiscussionContext } from '../../common/context';
 import { selectBlackoutDate } from '../../data/selectors';
 import { fetchThread } from '../../posts/data/thunks';
 import { inBlackoutDateRange } from '../../utils';
@@ -39,7 +40,9 @@ function Comment({
   const hasMorePages = useSelector(selectCommentHasMorePages(comment.id));
   const currentPage = useSelector(selectCommentCurrentPage(comment.id));
   const blackoutDateRange = useSelector(selectBlackoutDate);
-
+  const {
+    courseId,
+  } = useContext(DiscussionContext);
   useEffect(() => {
     // If the comment has a parent comment, it won't have any children, so don't fetch them.
     if (hasChildren && !currentPage && showFullThread) {
@@ -51,7 +54,7 @@ function Comment({
     [ContentActions.EDIT_CONTENT]: () => setEditing(true),
     [ContentActions.ENDORSE]: async () => {
       await dispatch(editComment(comment.id, { endorsed: !comment.endorsed }, ContentActions.ENDORSE));
-      await dispatch(fetchThread(comment.threadId));
+      await dispatch(fetchThread(comment.threadId, courseId));
     },
     [ContentActions.DELETE]: showDeleteConfirmation,
     [ContentActions.REPORT]: () => dispatch(editComment(comment.id, { flagged: !comment.abuseFlagged })),
diff --git a/src/discussions/comments/messages.js b/src/discussions/comments/messages.js
index 3fe4a355..85838798 100644
--- a/src/discussions/comments/messages.js
+++ b/src/discussions/comments/messages.js
@@ -182,6 +182,11 @@ const messages = defineMessages({
     defaultMessage: '{time} ago',
     description: 'Time text for endorse banner',
   },
+  noThreadFound: {
+    id: 'discussion.thread.notFound',
+    defaultMessage: 'Thread not found',
+    description: 'message to show on screen if the request thread is not found in course',
+  },
 });
 
 export default messages;
diff --git a/src/discussions/posts/data/api.js b/src/discussions/posts/data/api.js
index ed8c6328..04f2b326 100644
--- a/src/discussions/posts/data/api.js
+++ b/src/discussions/posts/data/api.js
@@ -71,8 +71,8 @@ export async function getThreads(
  * @param {string} threadId
  * @returns {Promise<{}>}
  */
-export async function getThread(threadId) {
-  const params = { requested_fields: 'profile_image' };
+export async function getThread(threadId, courseId) {
+  const params = { requested_fields: 'profile_image', course_id: courseId };
   const url = `${threadsApiUrl}${threadId}/`;
   const { data } = await getAuthenticatedHttpClient().get(url, { params });
   return data;
diff --git a/src/discussions/posts/data/thunks.js b/src/discussions/posts/data/thunks.js
index 04269def..7b3f2665 100644
--- a/src/discussions/posts/data/thunks.js
+++ b/src/discussions/posts/data/thunks.js
@@ -154,18 +154,18 @@ export function fetchThreads(courseId, {
   };
 }
 
-export function fetchThread(threadId, isDirectLinkPost = false) {
+export function fetchThread(threadId, courseId, isDirectLinkPost = false) {
   return async (dispatch) => {
     try {
       dispatch(fetchThreadRequest({ threadId }));
-      const data = await getThread(threadId);
+      const data = await getThread(threadId, courseId);
       if (isDirectLinkPost) {
         dispatch(fetchThreadByDirectLinkSuccess({ ...normaliseThreads(camelCaseObject(data)), page: 1 }));
       } else {
         dispatch(fetchThreadSuccess(normaliseThreads(camelCaseObject(data))));
       }
     } catch (error) {
-      if (getHttpErrorStatus(error) === 403) {
+      if (getHttpErrorStatus(error) === 403 || getHttpErrorStatus(error) === 404) {
         dispatch(fetchThreadDenied());
       } else {
         dispatch(fetchThreadFailed());
diff --git a/src/discussions/posts/post-editor/PostEditor.jsx b/src/discussions/posts/post-editor/PostEditor.jsx
index 74c5f918..0ab48773 100644
--- a/src/discussions/posts/post-editor/PostEditor.jsx
+++ b/src/discussions/posts/post-editor/PostEditor.jsx
@@ -33,6 +33,7 @@ import {
   selectUserIsGroupTa,
   selectUserIsStaff,
 } from '../../data/selectors';
+import { EmptyPage } from '../../empty-posts';
 import { selectCoursewareTopics, selectNonCoursewareIds, selectNonCoursewareTopics } from '../../topics/data/selectors';
 import {
   discussionsPath, formikCompatibleHandler, isFormikFieldInvalid, useCommentsPagePath,
@@ -193,16 +194,25 @@ function PostEditor({
       dispatch(fetchCourseCohorts(courseId));
     }
     if (editExisting) {
-      dispatch(fetchThread(postId));
+      dispatchSubmit(fetchThread(postId, courseId));
     }
   }, [courseId, editExisting]);
 
   if (editExisting && !post) {
-    return (
-      <div className="m-4 card p-4 align-items-center">
-        <Spinner animation="border" variant="primary" />
-      </div>
-    );
+    if (submitting) {
+      return (
+        <div className="m-4 card p-4 align-items-center">
+          <Spinner animation="border" variant="primary" />
+        </div>
+      );
+    }
+    if (!submitting) {
+      return (
+        <EmptyPage
+          title={intl.formatMessage(messages.noThreadFound)}
+        />
+      );
+    }
   }
 
   const validationSchema = Yup.object().shape({
diff --git a/src/discussions/posts/post-editor/messages.js b/src/discussions/posts/post-editor/messages.js
index c5b56362..240228ac 100644
--- a/src/discussions/posts/post-editor/messages.js
+++ b/src/discussions/posts/post-editor/messages.js
@@ -131,6 +131,11 @@ const messages = defineMessages({
     defaultMessage: 'Unnamed subcategory',
     description: 'display string for topics with missing names',
   },
+  noThreadFound: {
+    id: 'discussion.thread.notFound',
+    defaultMessage: 'Thread not found',
+    description: 'message to show on screen if the request thread is not found in course',
+  },
 });
 
 export default messages;