diff --git a/tst/Bootstrap.php b/tst/Bootstrap.php
index 59fb4060..bee35847 100644
--- a/tst/Bootstrap.php
+++ b/tst/Bootstrap.php
@@ -1,5 +1,7 @@
 <?php declare(strict_types=1);
 
+use Exception;
+use GlobIterator;
 use Google\Cloud\Core\Exception\BadRequestException;
 use Google\Cloud\Core\Exception\NotFoundException;
 use Google\Cloud\Storage\Bucket;
@@ -371,31 +373,34 @@ class Helper
      */
     public static function updateSubresourceIntegrity()
     {
-        $dir = dir(PATH . 'js');
-        while (false !== ($file = $dir->read())) {
-            if (substr($file, -3) === '.js') {
-                self::$hashes[$file] = base64_encode(
-                    hash('sha512', file_get_contents(
-                        PATH . 'js' . DIRECTORY_SEPARATOR . $file
-                    ), true)
-                );
+        foreach (new GlobIterator(PATH . 'js' . DIRECTORY_SEPARATOR . '*.js') as $file) {
+            if ($file->getBasename() == 'common.js') {
+                continue; // ignore JS unit test bootstrap
             }
+            self::$hashes[$file->getBasename()] = base64_encode(
+                hash('sha512', file_get_contents($file->getPathname()), true)
+            );
         }
 
+        $counter = 0;
         $file    = PATH . 'lib' . DIRECTORY_SEPARATOR . 'Configuration.php';
         $content = preg_replace_callback(
             '#\'js/([a-z0-9.-]+.js)(\' +)=\> \'[^\']*\',#',
-            function ($matches) {
+            function ($matches) use (&$counter) {
                 if (array_key_exists($matches[1], Helper::$hashes)) {
+                    $counter++;
                     return '\'js/' . $matches[1] . $matches[2] .
                         '=> \'sha512-' . Helper::$hashes[$matches[1]] . '\',';
                 } else {
-                    return $matches[0];
+                    throw new Exception('SRI hash for file js/' . $matches[1] . ' not found, please add the missing file or remove it from lib/Configuration.php.');
                 }
             },
             file_get_contents($file)
         );
         file_put_contents($file, $content);
+        if ($counter != count(self::$hashes)) {
+            throw new Exception('Mismatch between ' . count(self::$hashes) . ' found js files and ' . $counter . ' SRI hashes in lib/Configuration.php, please update lib/Configuration.php to match the list of js files.');
+        }
     }
 }