core/modules/rest/src/Entity/RestResourceConfig.php            | 10 ++++++++++
 core/modules/rest/src/Tests/RESTTestBase.php                   |  3 +--
 .../src/Functional/EntityResource/EntityResourceTestBase.php   |  3 ---
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/core/modules/rest/src/Entity/RestResourceConfig.php b/core/modules/rest/src/Entity/RestResourceConfig.php
index bb83584..60fe55a 100644
--- a/core/modules/rest/src/Entity/RestResourceConfig.php
+++ b/core/modules/rest/src/Entity/RestResourceConfig.php
@@ -3,6 +3,7 @@
 namespace Drupal\rest\Entity;
 
 use Drupal\Core\Config\Entity\ConfigEntityBase;
+use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Plugin\DefaultSingleLazyPluginCollection;
 use Drupal\rest\RestResourceConfigInterface;
 
@@ -255,4 +256,13 @@ protected function normalizeRestMethod($method) {
     return strtoupper($method);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function postSave(EntityStorageInterface $storage, $update = TRUE) {
+    parent::postSave($storage, $update);
+
+    \Drupal::service('router.builder')->setRebuildNeeded();
+  }
+
 }
diff --git a/core/modules/rest/src/Tests/RESTTestBase.php b/core/modules/rest/src/Tests/RESTTestBase.php
index 271df51..405493b 100644
--- a/core/modules/rest/src/Tests/RESTTestBase.php
+++ b/core/modules/rest/src/Tests/RESTTestBase.php
@@ -420,8 +420,7 @@ protected function enableService($resource_type, $method = 'GET', $format = NULL
    * Rebuilds routing caches.
    */
   protected function rebuildCache() {
-    // Rebuild routing cache, so that the REST API paths are available.
-    $this->container->get('router.builder')->rebuild();
+    $this->container->get('router.builder')->rebuildIfNeeded();
   }
 
   /**
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 973f5b9..02011ca 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -196,9 +196,6 @@ public function setUp() {
       }
       $this->entity->save();
     }
-
-    // @todo Remove this in https://www.drupal.org/node/2815845.
-    drupal_flush_all_caches();
   }
 
   /**