.../tests/src/Functional/EntityResource/EntityResourceTestBase.php     | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 158385b..60de61a 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -311,7 +311,8 @@ public function testPost() {
     $parseable_valid_request_body   = $this->serializer->encode($this->getNormalizedEntityToCreate(), static::$format);
     $parseable_valid_request_body_2 = $this->serializer->encode($this->getNormalizedEntityToCreate(), static::$format);
     $parseable_invalid_request_body   = $this->serializer->encode($this->getInvalidNormalizedEntityToCreate(), static::$format);
-    $parseable_invalid_request_body_2 = $this->serializer->encode($this->getNormalizedEntityToCreate() + ['uuid' => $this->randomMachineName(129)], static::$format);
+    // @todo Change to ['uuid' => UUID] when https://www.drupal.org/node/2820743 lands.
+    $parseable_invalid_request_body_2 = $this->serializer->encode($this->getNormalizedEntityToCreate() + ['uuid' => [['value' => $this->randomMachineName(129)]]], static::$format);
 
     // The URL and Guzzle request options that will be used in this test. The
     // request options will be modified/expanded throughout this test: