diff --git a/wp-includes/post-template.php b/wp-includes/post-template.php
index 5add75927..d3fd44025 100644
--- a/wp-includes/post-template.php
+++ b/wp-includes/post-template.php
@@ -304,6 +304,9 @@ function get_post_class( $class = '', $post_id = null ) {
 
 	$classes = array();
 
+	if ( empty($post) )
+		return $classes;
+
 	$classes[] = 'post-' . $post->ID;
 	$classes[] = $post->post_type;