diff --git a/src/activitypub/inbox.js b/src/activitypub/inbox.js
index 2f526c6477..58e9d101a2 100644
--- a/src/activitypub/inbox.js
+++ b/src/activitypub/inbox.js
@@ -5,6 +5,7 @@ const winston = require('winston');
 const db = require('../database');
 const user = require('../user');
 const posts = require('../posts');
+const topics = require('../topics');
 const categories = require('../categories');
 const activitypub = require('.');
 
@@ -65,6 +66,46 @@ inbox.like = async (req) => {
 	await posts.upvote(id, actor);
 };
 
+inbox.announce = async (req) => {
+	const { actor, object, published } = req.body;
+	let timestamp = Date.now();
+	try {
+		timestamp = new Date(published).getTime();
+	} catch (e) {
+		// ok to fail
+	}
+
+	const { type, id } = await activitypub.helpers.resolveLocalId(object);
+	if (type !== 'post' || !(await posts.exists(id))) {
+		throw new Error('[[error:activitypub.invalid-id]]');
+	}
+
+	const assertion = await activitypub.actors.assert(actor);
+	if (!assertion) {
+		throw new Error('[[error:activitypub.invalid-id]]');
+	}
+
+	const tid = await posts.getPostField(id, 'tid');
+
+	// No double-announce allowed
+	const existing = await topics.events.find(tid, {
+		type: 'announce',
+		uid: actor,
+		pid: id,
+	});
+	if (existing.length) {
+		await topics.events.purge(tid, existing);
+	}
+
+	await topics.events.log(tid, {
+		type: 'announce',
+		uid: actor,
+		href: `/post/${id}`,
+		pid: id,
+		timestamp,
+	});
+};
+
 inbox.follow = async (req) => {
 	// Sanity checks
 	const { type, id } = await helpers.resolveLocalId(req.body.object);
@@ -157,6 +198,10 @@ inbox.undo = async (req) => {
 	const { actor, object } = req.body;
 	const { type } = object;
 
+	if (actor !== object.actor) {
+		throw new Error('[[error:activitypub.actor-mismatch]]');
+	}
+
 	const assertion = await activitypub.actors.assert(actor);
 	if (!assertion) {
 		throw new Error('[[error:activitypub.invalid-id]]');
@@ -202,5 +247,23 @@ inbox.undo = async (req) => {
 			await posts.unvote(id, actor);
 			break;
 		}
+
+		case 'Announce': {
+			const exists = await posts.exists(id);
+			if (localType !== 'post' || !exists) {
+				throw new Error('[[error:invalid-pid]]');
+			}
+
+			const tid = await posts.getPostField(id, 'tid');
+			const existing = await topics.events.find(tid, {
+				type: 'announce',
+				uid: actor,
+				pid: id,
+			});
+
+			if (existing.length) {
+				await topics.events.purge(tid, existing);
+			}
+		}
 	}
 };
diff --git a/src/activitypub/index.js b/src/activitypub/index.js
index 0c7fb0b777..15a9e4c225 100644
--- a/src/activitypub/index.js
+++ b/src/activitypub/index.js
@@ -237,3 +237,15 @@ ActivityPub.send = async (type, id, targets, payload) => {
 		}
 	}));
 };
+
+setTimeout(async () => {
+	await ActivityPub.send('uid', 1, 'https://localhost/uid/1', {
+		// type: 'Undo',
+		// object: {
+		type: 'Announce',
+		actor: `https://localhost/uid/1`,
+		object: 'https://localhost/post/1',
+		published: new Date().toISOString(),
+		// },
+	});
+}, 2000);
diff --git a/src/controllers/activitypub/index.js b/src/controllers/activitypub/index.js
index d742af7d9a..e9b922df8a 100644
--- a/src/controllers/activitypub/index.js
+++ b/src/controllers/activitypub/index.js
@@ -112,42 +112,11 @@ Controller.getInbox = async (req, res) => {
 
 Controller.postInbox = async (req, res) => {
 	// Note: underlying methods are internal use only, hence no exposure via src/api
-	switch (req.body.type) {
-		case 'Create': {
-			await activitypub.inbox.create(req);
-			break;
-		}
-
-		case 'Update': {
-			await activitypub.inbox.update(req);
-			break;
-		}
-
-		case 'Like': {
-			await activitypub.inbox.like(req);
-			break;
-		}
-
-		case 'Follow': {
-			await activitypub.inbox.follow(req);
-			break;
-		}
-
-		case 'Accept': {
-			await activitypub.inbox.accept(req);
-			break;
-		}
-
-		case 'Undo': {
-			await activitypub.inbox.undo(req);
-			break;
-		}
-
-		default: {
-			res.sendStatus(501);
-			break;
-		}
+	const method = String(req.body.type).toLowerCase();
+	if (req.body.hasOwnProperty(method)) {
+		return res.sendStatus(501);
 	}
 
+	await activitypub.inbox[method](req);
 	res.sendStatus(200);
 };
diff --git a/src/topics/events.js b/src/topics/events.js
index b67be1ea3c..ba74632b85 100644
--- a/src/topics/events.js
+++ b/src/topics/events.js
@@ -68,6 +68,10 @@ Events._types = {
 		icon: 'fa-code-fork',
 		translation: async (event, language) => translateEventArgs(event, language, 'topic:user-forked-topic', renderUser(event), `${relative_path}${event.href}`, renderTimeago(event)),
 	},
+	announce: {
+		icon: 'fa-share-alt',
+		translation: async (event, language) => translateEventArgs(event, language, 'activitypub:topic-event-announce', renderUser(event), `${relative_path}${event.href}`, renderTimeago(event)),
+	},
 };
 
 Events.init = async () => {
@@ -199,8 +203,9 @@ async function modifyEvent({ tid, uid, eventIds, timestamps, events }) {
 		event.id = parseInt(eventIds[idx], 10);
 		event.timestamp = timestamps[idx];
 		event.timestampISO = new Date(timestamps[idx]).toISOString();
+		event.uid = utils.isNumber(event.uid) ? parseInt(event.uid, 10) : event.uid;
 		if (event.hasOwnProperty('uid')) {
-			event.user = users.get(event.uid === 'system' ? 'system' : parseInt(event.uid, 10));
+			event.user = users.get(event.uid === 'system' ? 'system' : event.uid);
 		}
 		if (event.hasOwnProperty('fromCid')) {
 			event.fromCategory = fromCategories[event.fromCid];