Index: wp-includes/classes.php
===================================================================
--- wp-includes/classes.php	(revision 15068)
+++ wp-includes/classes.php	(working copy)
@@ -145,7 +145,7 @@
 		// Fetch the rewrite rules.
 		$rewrite = $wp_rewrite->wp_rewrite_rules();
 
-		if ( ! empty($rewrite) ) {
+		if ( ! empty($rewrite) && defined( 'WP_USE_THEMES' ) && WP_USE_THEMES ) {
 			// If we match a rewrite rule, this will be cleared.
 			$error = '404';
 			$this->did_permalink = true;