Ticket #38076: 38076.diff

wp-admin/admin-header.php

@@ -35 +35 @@
 $title = strip_tags( $title );
 
 if ( is_network_admin() ) {
+
+    /*
+     * If multisite is not enabled, the get_network function is not available.
+     * We perform a multisite check to prevent a fatal error.
+     */
+    if ( ! is_multisite() ) {
+        wp_redirect( admin_url() );
+        exit;
+    }
         /* translators: Network admin screen title. %s: Network title. */
         $admin_title = sprintf( __( 'Network Admin: %s' ), get_network()->site_name );
 } elseif ( is_user_admin() ) {