diff --git a/src/Schema.php b/src/Schema.php
index c5f885e..526f582 100644
--- a/src/Schema.php
+++ b/src/Schema.php
@@ -664,7 +664,7 @@ private function processObject($data, Context $options, $path, $result = null)
                 $refProperty = null;
                 $dereference = true;
 
-                if (isset($array[self::PROP_REF])) {
+                if ($this->properties !== null && isset($array[self::PROP_REF])) {
                     $refProperty = $this->properties[self::PROP_REF];
 
                     if (isset($refProperty) && ($refProperty->format !== Format::URI_REFERENCE)) {