diff --git a/assert.php b/assert.php
index a71f57f..5903e1c 100644
--- a/assert.php
+++ b/assert.php
@@ -3,7 +3,7 @@
 class Assert {
   public static function type(array $a, $class) {
     foreach ($a as $item) {
-      if (get_class($item) !== $class) {
+      if (get_class($item) !== $class && !is_subclass_of($item, $class)) {
         throw new TypeException("$item is not of type $class");
       }
     }