diff --git a/wp-includes/rewrite.php b/wp-includes/rewrite.php
index 6eecf6a5a..69c76a853 100644
--- a/wp-includes/rewrite.php
+++ b/wp-includes/rewrite.php
@@ -1060,6 +1060,8 @@ class WP_Rewrite {
 	 * @return string|bool False if not found. Permalink structure string.
 	 */
 	function get_extra_permastruct($name) {
+		if ( empty($this->permalink_structure) )
+			return false;
 		if ( isset($this->extra_permastructs[$name]) )
 			return $this->extra_permastructs[$name];
 		return false;