diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 669382d96e..11dff750d9 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -549,12 +549,14 @@ public function testGet() {
     if ($this->entity->getEntityType()->getLinkTemplates()) {
       $this->assertArrayHasKey('Link', $response->getHeaders());
       $link_relation_type_manager = $this->container->get('plugin.manager.link_relation_type');
-      $expected_link_relation_headers = array_map(function ($relation_name) use ($link_relation_type_manager) {
+      $expected_link_relation_headers = array_values(array_map(function ($relation_name) use ($link_relation_type_manager) {
         $link_relation_type = $link_relation_type_manager->createInstance($relation_name);
         return $link_relation_type->isRegistered()
           ? $link_relation_type->getRegisteredName()
           : $link_relation_type->getExtensionUri();
-      }, array_keys($this->entity->getEntityType()->getLinkTemplates()));
+      }, array_filter(array_keys($this->entity->getEntityType()->getLinkTemplates()), function ($it) use ($link_relation_type_manager) {
+        return $link_relation_type_manager->hasDefinition($it);
+      })));
       $parse_rel_from_link_header = function ($value) use ($link_relation_type_manager) {
         $matches = [];
         if (preg_match('/rel="([^"]+)"/', $value, $matches) === 1) {