diff --git a/includes/functions.php b/includes/functions.php
index 7065edb01..b75bcc82d 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -1478,12 +1478,22 @@ function get_attribution_domains() {
  * @return string The upload base URL.
  */
 function get_upload_baseurl() {
-	$upload_dir = \wp_get_upload_dir();
+	/**
+	 * 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_upload_dir();
 
 	/**
 	 * Filters the upload base URL.
 	 *
-	 * @param string \wp_get_upload_dir()['baseurl'] The upload base URL.
+	 * @param string \wp_upload_dir()['baseurl'] The upload base URL.
 	 */
 	return apply_filters( 'activitypub_get_upload_baseurl', $upload_dir['baseurl'] );
 }