diff --git src/bp-activity/bp-activity-actions.php src/bp-activity/bp-activity-actions.php
index d17ed65..e6e466f 100644
--- src/bp-activity/bp-activity-actions.php
+++ src/bp-activity/bp-activity-actions.php
@@ -348,12 +348,14 @@ function bp_activity_action_post_update() {
 		 * Filters activity object for BuddyPress core and plugin authors before posting activity update.
 		 *
 		 * @since 1.2.0
+		 * @since 2.4.0 Add $activity_id argument
 		 *
-		 * @param string $object  Activity item being associated to.
-		 * @param string $item_id Component ID being posted to.
-		 * @param string $content Activity content being posted.
+		 * @param int|bool   $activity_id   The activity ID. False otherwise.
+		 * @param string     $object        Object type being associated to.
+		 * @param string     $item_id       Single item ID being posted to.
+		 * @param string     $content       Activity content being posted.
 		 */
-		$activity_id = apply_filters( 'bp_activity_custom_update', $object, $item_id, $content );
+		$activity_id = apply_filters( 'bp_activity_custom_update', false, $object, $item_id, $content );
 	}
 
 	// Provide user feedback