diff --git a/tests/Fixtures/SimpleObjectProxy.php b/tests/Fixtures/SimpleObjectProxy.php
index 50d0d05..a921bfe 100644
--- a/tests/Fixtures/SimpleObjectProxy.php
+++ b/tests/Fixtures/SimpleObjectProxy.php
@@ -13,7 +13,7 @@
 use Doctrine\Common\Persistence\Proxy as CommonProxy;
 use Doctrine\Persistence\Proxy;
 
-if (class_exists(CommonProxy::class)) {
+if (interface_exists(CommonProxy::class)) {
     class SimpleObjectProxy extends SimpleObject implements CommonProxy
     {
         /**