diff --git a/CHANGELOG.md b/CHANGELOG.md
index 851c56a20..8c125eb13 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+* A `pre_activitypub_get_upload_baseurl` filter
 * Fediverse Preview on post-overview page
 * GitHub action to enforce Changelog updates.
 
diff --git a/activitypub.php b/activitypub.php
index b4d8fea2b..6286e921a 100644
--- a/activitypub.php
+++ b/activitypub.php
@@ -3,7 +3,7 @@
  * Plugin Name: ActivityPub
  * Plugin URI: https://github.com/pfefferle/wordpress-activitypub/
  * Description: The ActivityPub protocol is a decentralized social networking protocol based upon the ActivityStreams 2.0 data format.
- * Version: 4.2.1
+ * Version: 4.2.2
  * Author: Matthias Pfefferle & Automattic
  * Author URI: https://automattic.com/
  * License: MIT
@@ -19,7 +19,7 @@
 
 use WP_CLI;
 
-\define( 'ACTIVITYPUB_PLUGIN_VERSION', '4.2.1' );
+\define( 'ACTIVITYPUB_PLUGIN_VERSION', '4.2.2' );
 
 // Plugin related constants.
 \define( 'ACTIVITYPUB_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
diff --git a/includes/functions.php b/includes/functions.php
index 7065edb01..9cc1b8aa5 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -1478,6 +1478,16 @@ function get_attribution_domains() {
  * @return string The upload base URL.
  */
 function get_upload_baseurl() {
+	/**
+	 * Early filter to allow plugins to set the upload base URL.
+	 *
+	 * @param string|false $maybe_upload_dir The upload base URL or false if not set.
+	 */
+	$maybe_upload_dir = apply_filters( 'pre_activitypub_get_upload_baseurl', false );
+	if ( false !== $maybe_upload_dir ) {
+		return $maybe_upload_dir;
+	}
+
 	$upload_dir = \wp_get_upload_dir();
 
 	/**
diff --git a/readme.txt b/readme.txt
index d33d59a4c..011220948 100644
--- a/readme.txt
+++ b/readme.txt
@@ -134,6 +134,7 @@ For reasons of data protection, it is not possible to see the followers of other
 
 = Dev =
 
+* Added: A `pre_activitypub_get_upload_baseurl` filter
 * Added: Fediverse Preview on post-overview page
 * Added: GitHub action to enforce Changelog updates.
 * Improved: Outsource Constants to a separate file