diff --git a/src/activitypub/actors.js b/src/activitypub/actors.js
index b13f35ed18..e581801136 100644
--- a/src/activitypub/actors.js
+++ b/src/activitypub/actors.js
@@ -410,6 +410,7 @@ async function _migratePersonToGroup(categoryObjs) {
 }
 
 Actors.getLocalFollowers = async (id) => {
+	// Returns local uids and cids that follow a remote actor (by id)
 	const response = {
 		uids: new Set(),
 		cids: new Set(),
@@ -419,15 +420,27 @@ Actors.getLocalFollowers = async (id) => {
 		return response;
 	}
 
-	const members = await db.getSortedSetMembers(`followersRemote:${id}`);
+	const [isUser, isCategory] = await Promise.all([
+		user.exists(id),
+		categories.exists(id),
+	]);
 
-	members.forEach((id) => {
-		if (utils.isNumber(id)) {
-			response.uids.add(parseInt(id, 10));
-		} else if (id.startsWith('cid|') && utils.isNumber(id.slice(4))) {
-			response.cids.add(parseInt(id.slice(4), 10));
-		}
-	});
+	if (isUser) {
+		const members = await db.getSortedSetMembers(`followersRemote:${id}`);
+
+		members.forEach((id) => {
+			if (utils.isNumber(id)) {
+				response.uids.add(parseInt(id, 10));
+			} else if (id.startsWith('cid|') && utils.isNumber(id.slice(4))) {
+				response.cids.add(parseInt(id.slice(4), 10));
+			}
+		});
+	} else if (isCategory) {
+		const members = await db.getSortedSetRangeByScore(`cid:${id}:uid:watch:state`, 0, -1, categories.watchStates.tracking, categories.watchStates.watching);
+		members.forEach((uid) => {
+			response.uids.add(uid);
+		});
+	}
 
 	return response;
 };
diff --git a/src/activitypub/notes.js b/src/activitypub/notes.js
index eafb1f8cb6..be0b61f847 100644
--- a/src/activitypub/notes.js
+++ b/src/activitypub/notes.js
@@ -462,6 +462,12 @@ Notes.syncUserInboxes = async function (tid, uid) {
 		uids.add(uid);
 	});
 
+	// Category followers
+	const categoryFollowers = await activitypub.actors.getLocalFollowers(cid);
+	categoryFollowers.uids.forEach((uid) => {
+		uids.add(uid);
+	});
+
 	const keys = Array.from(uids).map(uid => `uid:${uid}:inbox`);
 	const score = await db.sortedSetScore(`cid:${cid}:tids`, tid);
 
diff --git a/src/user/index.js b/src/user/index.js
index 35c3e67f3e..2059621f6d 100644
--- a/src/user/index.js
+++ b/src/user/index.js
@@ -46,8 +46,12 @@ User.exists = async function (uids) {
 	const singular = !Array.isArray(uids);
 	uids = singular ? [uids] : uids;
 
-	let results = await Promise.all(uids.map(async uid => await db.isMemberOfSortedSets(['users:joindate', 'usersRemote:lastCrawled'], uid)));
-	results = results.map(set => set.some(Boolean));
+	const local = await db.isSortedSetMembers('users:joindate', uids);
+	const remote = await db.exists(uids.map(uid => `userRemote:${uid}`));
+	const results = local.map((a, idx) => {
+		const b = remote[idx];
+		return a || b;
+	});
 
 	return singular ? results.pop() : results;
 };
diff --git a/test/activitypub/notes.js b/test/activitypub/notes.js
index c9c5e42e7b..5157bc5645 100644
--- a/test/activitypub/notes.js
+++ b/test/activitypub/notes.js
@@ -109,6 +109,22 @@ describe('Notes', () => {
 						assert.strictEqual(category[prop], 1);
 					});
 				});
+
+				it('should add a remote category topic to a user\'s inbox if they are following the category', async () => {
+					const { id: cid, actor } = helpers.mocks.group();
+					await activitypub.actors.assertGroup([cid]);
+
+					const uid = await user.create({ username: utils.generateUUID() });
+					await api.categories.setWatchState({ uid }, { cid, state: categories.watchStates.tracking });
+
+					const { id } = helpers.mocks.note({
+						cc: [cid],
+					});
+					const { tid } = await activitypub.notes.assert(0, id);
+
+					const inInbox = await db.isSortedSetMember(`uid:${uid}:inbox`, tid);
+					assert(inInbox);
+				});
 			});
 
 			describe('User-specific behaviours', () => {