diff --git a/tests/classes/bug24399.phpt b/tests/classes/bug24399.phpt
new file mode 100644
index 00000000000..f0cf9edb7b3
--- /dev/null
+++ b/tests/classes/bug24399.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Bug #24399: is_subclass_of() crashes when parent class doesn't exist.
+--SKIPIF--
+<?php if (version_compare(zend_version(), '2.0.0-dev', '<')) die('skip ZendEngine 2 needed'); ?>
+--FILE--
+<?php
+class dooh {
+    var $blah;
+}
+$d = new dooh;
+var_dump(is_subclass_of($d, 'dooh'));
+?>
+--EXPECT--
+bool(false)