diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index 215494fe6e..1a7ab30266 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -1053,6 +1053,7 @@ class wpdb {
 		if ( is_null( $query ) )
 			return;
 
+		// This is not meant to be foolproof -- but it will catch obviously incorrect usage.
 		if ( strpos( $query, '%' ) === false ) {
 			_doing_it_wrong( 'wpdb::prepare', sprintf( __( 'The query argument of %s must have a placeholder.' ), 'wpdb::prepare()' ), '3.9' );
 		}