diff --git a/app/lib/activitypub/activity.rb b/app/lib/activitypub/activity.rb
index 29411774a1..0c98651d12 100644
--- a/app/lib/activitypub/activity.rb
+++ b/app/lib/activitypub/activity.rb
@@ -130,12 +130,7 @@ class ActivityPub::Activity
 
   def first_mentioned_local_account
     audience = (as_array(@json['to']) + as_array(@json['cc'])).map { |x| value_or_id(x) }.uniq
-    local_usernames = audience.select { |uri| ActivityPub::TagManager.instance.local_uri?(uri) }
-                              .map { |uri| ActivityPub::TagManager.instance.uri_to_local_id(uri, :username) }
-
-    return if local_usernames.empty?
-
-    Account.local.where(username: local_usernames).first
+    ActivityPub::TagManager.instance.uris_to_local_accounts(audience).first
   end
 
   def first_local_follower
diff --git a/app/lib/activitypub/activity/create.rb b/app/lib/activitypub/activity/create.rb
index f54e64ad7e..4b2549ba96 100644
--- a/app/lib/activitypub/activity/create.rb
+++ b/app/lib/activitypub/activity/create.rb
@@ -412,11 +412,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   def addresses_local_accounts?
     return true if @options[:delivered_to_account_id]
 
-    local_usernames = (audience_to + audience_cc).uniq.select { |uri| ActivityPub::TagManager.instance.local_uri?(uri) }.map { |uri| ActivityPub::TagManager.instance.uri_to_local_id(uri, :username) }
-
-    return false if local_usernames.empty?
-
-    Account.local.exists?(username: local_usernames)
+    ActivityPub::TagManager.instance.uris_to_local_accounts((audience_to + audience_cc).uniq).exists?
   end
 
   def tombstone_exists?
diff --git a/app/lib/activitypub/tag_manager.rb b/app/lib/activitypub/tag_manager.rb
index 5cba9a8006..2fe707e79b 100644
--- a/app/lib/activitypub/tag_manager.rb
+++ b/app/lib/activitypub/tag_manager.rb
@@ -203,6 +203,19 @@ class ActivityPub::TagManager
     path_params[param]
   end
 
+  def uris_to_local_accounts(uris)
+    usernames = []
+    ids = []
+
+    uris.each do |uri|
+      param, value = uri_to_local_account_params(uri)
+      usernames << value.downcase if param == :username
+      ids << value if param == :id
+    end
+
+    Account.local.with_username(usernames).or(Account.local.where(id: ids))
+  end
+
   def uri_to_actor(uri)
     uri_to_resource(uri, Account)
   end
@@ -213,7 +226,7 @@ class ActivityPub::TagManager
     if local_uri?(uri)
       case klass.name
       when 'Account'
-        klass.find_local(uri_to_local_id(uri, :username))
+        uris_to_local_accounts([uri]).first
       else
         StatusFinder.new(uri).status
       end
@@ -225,4 +238,20 @@ class ActivityPub::TagManager
   rescue ActiveRecord::RecordNotFound
     nil
   end
+
+  private
+
+  def uri_to_local_account_params(uri)
+    return unless local_uri?(uri)
+
+    path_params = Rails.application.routes.recognize_path(uri)
+
+    # TODO: handle numeric IDs
+    case path_params[:controller]
+    when 'accounts'
+      [:username, path_params[:username]]
+    when 'instance_actors'
+      [:id, -99]
+    end
+  end
 end
diff --git a/app/services/activitypub/synchronize_followers_service.rb b/app/services/activitypub/synchronize_followers_service.rb
index 5b58a025cb..fd6fd1b899 100644
--- a/app/services/activitypub/synchronize_followers_service.rb
+++ b/app/services/activitypub/synchronize_followers_service.rb
@@ -30,10 +30,7 @@ class ActivityPub::SynchronizeFollowersService < BaseService
     # Account record, and should we not do that, we should have sent a Delete.
     # In any case there is not much we can do if that occurs.
 
-    # TODO: this will need changes when switching to numeric IDs
-
-    usernames = items.filter_map { |uri| ActivityPub::TagManager.instance.uri_to_local_id(uri, :username)&.downcase }
-    Account.local.with_username(usernames)
+    ActivityPub::TagManager.instance.uris_to_local_accounts(items)
   end
 
   def remove_unexpected_local_followers!
diff --git a/spec/lib/activitypub/tag_manager_spec.rb b/spec/lib/activitypub/tag_manager_spec.rb
index 4dcfc69824..7a4cf3c1b8 100644
--- a/spec/lib/activitypub/tag_manager_spec.rb
+++ b/spec/lib/activitypub/tag_manager_spec.rb
@@ -187,6 +187,23 @@ RSpec.describe ActivityPub::TagManager do
     end
   end
 
+  describe '#uris_to_local_accounts' do
+    it 'returns the expected local accounts' do
+      account = Fabricate(:account)
+      expect(subject.uris_to_local_accounts([subject.uri_for(account), instance_actor_url])).to contain_exactly(account, Account.representative)
+    end
+
+    it 'does not return remote accounts' do
+      account = Fabricate(:account, uri: 'https://example.com/123', domain: 'example.com')
+      expect(subject.uris_to_local_accounts([subject.uri_for(account)])).to be_empty
+    end
+
+    it 'does not return an account for a local post' do
+      status = Fabricate(:status)
+      expect(subject.uris_to_local_accounts([subject.uri_for(status)])).to be_empty
+    end
+  end
+
   describe '#uri_to_resource' do
     it 'returns the local account' do
       account = Fabricate(:account)