Index: ms-functions.php
===================================================================
--- ms-functions.php	(revision 23992)
+++ ms-functions.php	(working copy)
@@ -1607,11 +1607,18 @@
 }
 
 /**
- * Correct 404 redirects when NOBLOGREDIRECT is defined.
+ * Correct 404 redirects on subdirectory installs
+ * when NOBLOGREDIRECT is defined.
  *
  * @since MU
  */
 function maybe_redirect_404() {
+
+	// If we're running on a subdomain install, bail early
+	if ( is_subdomain_install() )
+		return;
+
+	// Otherwise, do the redirect
 	global $current_site;
 	if ( is_main_site() && is_404() && defined( 'NOBLOGREDIRECT' ) && ( $destination = apply_filters( 'blog_redirect_404', NOBLOGREDIRECT ) ) ) {
 		if ( $destination == '%siteurl%' )