diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 783bba0..00d6b61 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1320,6 +1320,13 @@ class DrupalWebTestCase extends DrupalTestCase {
     $test_info['test_run_id'] = $this->databasePrefix;
     $test_info['in_child_site'] = FALSE;
 
+    // Preset the 'install_profile' system variable, so the first call into
+    // system_rebuild_module_data() (in drupal_install_system()) will register
+    // the test's profile as a module. Without this, the installation profile of
+    // the parent site (executing the test) is registered, and the test
+    // profile's hook_install() and other hook implementations are never invoked.
+    $conf['install_profile'] = $this->profile;
+
     include_once DRUPAL_ROOT . '/includes/install.inc';
     drupal_install_system();