diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index f12b760..bdaeef6 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -634,7 +634,6 @@ public function testPost() {
     // missing ?_format query string.
     $response = $this->request('POST', $url, $request_options);
     $this->assertSame(415, $response->getStatusCode());
-    $this->assertSame(['text/plain; charset=UTF-8'], $response->getHeader('Content-Type'));
     $this->assertSame(['text/html; charset=UTF-8'], $response->getHeader('Content-Type'));
     $this->assertContains('A client error happened', (string) $response->getBody());