diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 966db3aad0..43b904cf7b 100644
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -464,26 +464,18 @@ function simpletest_script_init() {
   }
 
   // Detect if we're in the top-level process using the private 'execute-test'
-  // argument.
-  if (!$args['execute-test']) {
-    // Determine if the current user is likely to be able to run composer to
-    // update PHPUnit if necessary. There is no direct way in PHP of determining
-    // the user running the process, therefore create a file and check if the
-    // owner is the same as the owner of the current script. The important thing
-    // is to allow drupal.org's testing infrastructure to update PHPUnit
-    // automatically. In all other cases it is okay to emit the error message
-    // telling the user to do the upgrade themselves.
-    $tmp = tempnam(sys_get_temp_dir(), 'drupal');
-    if (fileowner($tmp) === getmyuid() && getmyuid() !== FALSE) {
-      // Update PHPUnit if needed and possible. There is a later check once the
-      // autoloader is in place to ensure we're on the correct version. We need to
-      // do this before the autoloader is in place to ensure that it is correct.
-      $composer = ($composer = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar`) : `which composer.phar`))
-        ? $php . ' ' . escapeshellarg($composer)
-        : 'composer';
-      passthru("$composer run-script drupal-phpunit-upgrade-check");
-    }
-    unlink($tmp);
+  // argument. Determine if being run on drupal.org's testing infrastructure
+  // using the DCI_JobType environmental variable so we can update PHPUnit
+  // automatically. In all other cases if an update is necessary, an error
+  // message will be emitted telling the user to do the upgrade themselves.
+  if (!$args['execute-test'] && getenv('DCI_JobType') !== FALSE) {
+    // Update PHPUnit if needed and possible. There is a later check once the
+    // autoloader is in place to ensure we're on the correct version. We need to
+    // do this before the autoloader is in place to ensure that it is correct.
+    $composer = ($composer = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar`) : `which composer.phar`))
+      ? $php . ' ' . escapeshellarg($composer)
+      : 'composer';
+    passthru("$composer run-script drupal-phpunit-upgrade-check");
   }
 
   $autoloader = require_once __DIR__ . '/../../autoload.php';