Index: src/wp-includes/query.php
===================================================================
--- src/wp-includes/query.php	(revision 30242)
+++ src/wp-includes/query.php	(working copy)
@@ -4071,22 +4071,29 @@
 	 * @return bool
 	 */
 	public function is_author( $author = '' ) {
-		if ( !$this->is_author )
+		if ( ! $this->is_author ) {
 			return false;
+		}
 
-		if ( empty($author) )
+		if ( empty( $author ) ) {
 			return true;
+		}
 
 		$author_obj = $this->get_queried_object();
 
+		if ( ! is_a( $author_obj, 'WP_User' ) ) {
+			return false;
+		}
+
 		$author = (array) $author;
 
-		if ( in_array( $author_obj->ID, $author ) )
+		if ( in_array( $author_obj->ID, $author ) ) {
 			return true;
-		elseif ( in_array( $author_obj->nickname, $author ) )
+		} elseif ( in_array( $author_obj->nickname, $author ) ) {
 			return true;
-		elseif ( in_array( $author_obj->user_nicename, $author ) )
+		} elseif ( in_array( $author_obj->user_nicename, $author ) ) {
 			return true;
+		}
 
 		return false;
 	}