diff --git a/src/Handler/UnionHandler.php b/src/Handler/UnionHandler.php
index 8e1f60009..5618cc40e 100644
--- a/src/Handler/UnionHandler.php
+++ b/src/Handler/UnionHandler.php
@@ -93,7 +93,7 @@ private function reorderTypes(array $type): array
         if ($type['params']) {
             uasort($type['params'], function($a, $b) {
                 $order = ['null' => 0, 'true' => 1, 'false' => 2, 'bool' => 3, 'int' => 4, 'float' => 5, 'string' => 6];
-                return $order[$a['name']] || 7 <=> $order[$b['name']] || 7;
+                return (array_key_exists($a['name'], $order) ? $order[$a['name']] : 7) <=> (array_key_exists($b['name'], $order) ? $order[$b['name']] : 7);
             });
         }
         return $type;