diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 16eec816b2..76401a0dd6 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1498,8 +1498,8 @@ class DrupalWebTestCase extends DrupalTestCase {
   protected function getSetupCacheKey($cache_key_prefix = '') {
     // The cache key needs to start with a numeric character, so that the cached
     // installation gets cleaned up properly.
-    $cache_key_prefix = hash('crc32b', $cache_key_prefix . $this->profile) . '_';
-    return '1c_' . $cache_key_prefix . $this->profile;
+    $cache_key_prefix = hash('crc32b', $cache_key_prefix . $this->profile);
+    return '1c' . $cache_key_prefix;
   }
 
   /**