diff --git a/Packer.php b/Packer.php
index 4c475924..cf364a50 100644
--- a/Packer.php
+++ b/Packer.php
@@ -63,6 +63,8 @@ public function addBox(Box $aBox) {
 
     /**
      * Pack items into boxes
+     *
+     * @throws \RuntimeException
      * @return PackedBox[]
      */
     public function pack() {