Index: wp-includes/general-template.php
===================================================================
--- wp-includes/general-template.php	(revision 37273)
+++ wp-includes/general-template.php	(working copy)
@@ -905,8 +905,11 @@
 	 * @since 4.5.0
 	 *
 	 * @param string $html Custom logo HTML output.
+	 * @param int $blog_id ID of the blog in question. Default is the ID of the current blog.
 	 */
-	return apply_filters( 'get_custom_logo', $html );
+	$html = apply_filters( 'get_custom_logo', $html, $blog_id );
+
+	return $html;
 }
 
 /**