Index: wp-includes/default-constants.php
===================================================================
--- wp-includes/default-constants.php	(revision 28860)
+++ wp-includes/default-constants.php	(working copy)
@@ -319,9 +319,18 @@
 	 * Slug of the default theme for this install.
 	 * Used as the default theme when installing new sites.
 	 * Will be used as the fallback if the current theme doesn't exist.
+         * Will use the latest theme if available, else the first theme which is returned by wp_get_themes().
 	 * @since 3.0.0
 	 */
-	if ( !defined('WP_DEFAULT_THEME') )
-		define( 'WP_DEFAULT_THEME', 'twentyfourteen' );
-
+	if ( !defined('WP_DEFAULT_THEME') ) {
+		if ( wp_get_theme('twentyfourteen')->exists() ) 		
+			define( 'WP_DEFAULT_THEME', 'twentyfourteen' );
+		else {
+			$themes = reset(wp_get_themes());
+			if ( $themes != false )
+				define( 'WP_DEFAULT_THEME', $themes->get_stylesheet() );
+			else
+				define( 'WP_DEFAULT_THEME', '' ); 
+		}
+	}
 }