Fix issue Yoast#492

inc/wpseo-non-ajax-functions.php

@@ -500,11 +500,12 @@ function allow_custom_field_edits( $allcaps, $cap, $args ) {
 
 	// Make sure the request is to edit or add a post meta (this is usually also the second value in $cap,
 	// but this is safer to check).
-	if ( in_array( $args[0], array( "edit_post_meta", "add_post_meta" ) ) ) {
+	if ( in_array( $args[0], array( 'edit_post_meta', 'add_post_meta' ) ) ) {
 		// Only allow editing rights for users who have the rights to edit this post and make sure
 		// the meta value starts with _yoast_wpseo.
-		if ( current_user_can( 'edit_post', $args[2] ) && ( ! empty( $args[3] ) && strpos( $args[3], "_yoast_wpseo_" ) === 0 ) )
+		if ( ( isset( $args[2] ) && current_user_can( 'edit_post', $args[2] ) ) && ( ( isset( $args[3] ) && $args[3] !== '' ) && strpos( $args[3], '_yoast_wpseo_' ) === 0 ) ) {
 			$allcaps[$args[0]] = true;
+		}
 	}
 
 	return $allcaps;

readme.txt

@@ -106,6 +106,11 @@ You'll find the [FAQ on Yoast.com](http://yoast.com/wordpress/seo/faq/).
 
 == Changelog ==
 
+= Trunk =
+
+* Bugfixes
+	* Fix issue with user capability authorisation check as reported by [scienceandpoetry](https://github.com/scienceandpoetry) in issue [#492](https://github.com/Yoast/wordpress-seo/issues/492) - props [Jrf](http://profiles.wordpress.org/jrf).
+
 = 1.4.22 =
 
 * Bugfixes