diff -u b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
--- b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
@@ -593,7 +593,7 @@
     $this->assertFileExists('public://foobar/example_6.cgi_.png_.txt');
 
     // Add .php as an allowed extension without .txt. Since insecure uploads are
-    // are not allowed, .php files will be rejected.
+    // not allowed, .php files will be rejected.
     $this->field->setSetting('file_extensions', 'php')->save();
     $this->refreshTestStateAfterRestConfigChange();