Index: src/wp-login.php
===================================================================
--- src/wp-login.php	(revision 36349)
+++ src/wp-login.php	(working copy)
@@ -671,16 +671,18 @@
 break;
 
 case 'register' :
-	if ( is_multisite() ) {
+	 if ( apply_filters( 'require_wp_signup', is_multisite() ) ) {
 		/**
-		 * Filter the Multisite sign up URL.
+		 * Filter the Multi-site sign up URL.
 		 *
 		 * @since 3.0.0
 		 *
 		 * @param string $sign_up_url The sign up URL.
 		 */
-		wp_redirect( apply_filters( 'wp_signup_location', network_site_url( 'wp-signup.php' ) ) );
-		exit;
+		if ( wp_redirect( apply_filters( 'wp_signup_location', network_site_url( 'wp-signup.php' ) ) ) ){
+			exit;
+		};
+
 	}
 
 	if ( !get_option('users_can_register') ) {