tests/src/Functional/ResourceTestBase.php | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tests/src/Functional/ResourceTestBase.php b/tests/src/Functional/ResourceTestBase.php
index 3670bef..6abb30f 100644
--- a/tests/src/Functional/ResourceTestBase.php
+++ b/tests/src/Functional/ResourceTestBase.php
@@ -1902,7 +1902,12 @@ abstract class ResourceTestBase extends BrowserTestBase {
     // DX: 405 when read-only mode is enabled.
     $response = $this->request('POST', $url, $request_options);
     $this->assertResourceErrorResponse(405, sprintf("JSON:API's read-only mode is enabled. Site administrators can enable writes at %s.", Url::fromUri('base:/admin/config/services/jsonapi')->setAbsolute()->toString(TRUE)->getGeneratedUrl()), $url, $response);
-    $this->assertSame(['GET'], $response->getHeader('Allow'));
+    if ($this->resourceType->isLocatable()) {
+      $this->assertSame(['GET'], $response->getHeader('Allow'));
+    }
+    else {
+      $this->assertSame([''], $response->getHeader('Allow'));
+    }
 
     $this->config('jsonapi.settings')->set('read_only', FALSE)->save(TRUE);