Index: src/wp-includes/load.php
===================================================================
--- src/wp-includes/load.php	(revision 27276)
+++ src/wp-includes/load.php	(working copy)
@@ -403,8 +403,9 @@
  	if ( ! function_exists( 'wp_cache_init' ) ) {
 		if ( file_exists( WP_CONTENT_DIR . '/object-cache.php' ) ) {
 			require_once ( WP_CONTENT_DIR . '/object-cache.php' );
-			if ( function_exists( 'wp_cache_init' ) )
+			if ( function_exists( 'wp_cache_init' ) && false !== wp_using_ext_object_cache() ) {
 				wp_using_ext_object_cache( true );
+			}
 		}
 
 		$first_init = true;