diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 2db30d956b6b4c34ed99d689aea316568f38fdf1..9e51cd4d6f162b16db3d677b208030fc1f4bc439 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -276,11 +276,13 @@ function simpletest_script_help() {
 
   --class     Run tests identified by specific class names, instead of group names.
               A specific test method can be added, for example,
-              'Drupal\book\Tests\BookTest::testBookExport'.
+              'Drupal\book\Tests\BookTest::testBookExport'. This argument must
+              be last on the command line.
 
   --file      Run tests identified by specific file names, instead of group names.
               Specify the path and the extension
-              (i.e. 'core/modules/user/user.test').
+              (i.e. 'core/modules/user/user.test'). This argument must be last
+              on the command line.
 
   --types