diff --git a/lib/SimpleSAML/Error/UnserializableException.php b/lib/SimpleSAML/Error/UnserializableException.php
index d843f70428699a2c2cd4afb0bb7fef184ef010a6..ea0bef5987f9435cdf85889f27cf4ca9b56e9fc9 100644
--- a/lib/SimpleSAML/Error/UnserializableException.php
+++ b/lib/SimpleSAML/Error/UnserializableException.php
@@ -40,6 +40,8 @@ class UnserializableException extends Exception
 
         $this->class = get_class($original);
         $msg = $original->getMessage();
+
+        /** @var string|int $code */
         $code = $original->getCode();
 
         if (!is_int($code)) {