diff --git a/src/activitypub/actors.js b/src/activitypub/actors.js
index 628246464e..6f25d67ae0 100644
--- a/src/activitypub/actors.js
+++ b/src/activitypub/actors.js
@@ -8,7 +8,10 @@ const user = require('../user');
 const utils = require('../utils');
 const TTLCache = require('../cache/ttl');
 
-const failedWebfingerCache = TTLCache({ ttl: 1000 * 60 * 10 }); // 10 minutes
+const failedWebfingerCache = TTLCache({
+	max: 5000,
+	ttl: 1000 * 60 * 10, // 10 minutes
+});
 
 const activitypub = module.parent.exports;
 
diff --git a/src/activitypub/helpers.js b/src/activitypub/helpers.js
index 967520ca3f..37a5fdbcc5 100644
--- a/src/activitypub/helpers.js
+++ b/src/activitypub/helpers.js
@@ -16,7 +16,10 @@ const user = require('../user');
 const activitypub = require('.');
 
 const webfingerRegex = /^(@|acct:)?[\w\-]+@.+$/;
-const webfingerCache = ttl({ ttl: 1000 * 60 * 60 * 24 }); // 24 hours
+const webfingerCache = ttl({
+	max: 5000,
+	ttl: 1000 * 60 * 60 * 24, // 24 hours
+});
 
 const Helpers = module.exports;
 
@@ -59,8 +62,9 @@ Helpers.query = async (id) => {
 		return false;
 	}
 
-	if (webfingerCache.has(id)) {
-		return webfingerCache.get(id);
+	const cached = webfingerCache.get(id);
+	if (cached !== undefined) {
+		return cached;
 	}
 
 	const query = new URLSearchParams({ resource: uri });
diff --git a/src/activitypub/index.js b/src/activitypub/index.js
index 0e46941bb7..25ddcbe3ef 100644
--- a/src/activitypub/index.js
+++ b/src/activitypub/index.js
@@ -15,7 +15,10 @@ const batch = require('../batch');
 const pubsub = require('../pubsub');
 const analytics = require('../analytics');
 
-const requestCache = ttl({ ttl: 1000 * 60 * 5 }); // 5 minutes
+const requestCache = ttl({
+	max: 5000,
+	ttl: 1000 * 60 * 5, // 5 minutes
+});
 const ActivityPub = module.exports;
 
 ActivityPub._constants = Object.freeze({
@@ -223,8 +226,9 @@ ActivityPub.verify = async (req) => {
 
 ActivityPub.get = async (type, id, uri) => {
 	const cacheKey = [id, uri].join(';');
-	if (requestCache.has(cacheKey)) {
-		return requestCache.get(cacheKey);
+	const cached = requestCache.get(cacheKey);
+	if (cached !== undefined) {
+		return cached;
 	}
 
 	const keyData = await ActivityPub.getPrivateKey(type, id);