diff --git a/lib/phpunit/classes/data_generator.php b/lib/phpunit/classes/data_generator.php
index 515f062ee24..bcc90fa19fd 100644
--- a/lib/phpunit/classes/data_generator.php
+++ b/lib/phpunit/classes/data_generator.php
@@ -157,9 +157,11 @@ EOD;
         }
 
         if (!isset($record['username'])) {
-            $record['username'] = textlib::strtolower($record['firstname']).textlib::strtolower($record['lastname']);
+            $record['username'] = 'username'.$i;
+            $j = 2;
             while ($DB->record_exists('user', array('username'=>$record['username'], 'mnethostid'=>$record['mnethostid']))) {
-                $record['username'] = $record['username'].'_'.$i;
+                $record['username'] = 'username'.$i.'_'.$j;
+                $j++;
             }
         }
 
diff --git a/lib/phpunit/tests/generator_test.php b/lib/phpunit/tests/generator_test.php
index 9c6f4f6bbae..1a3efc34aea 100644
--- a/lib/phpunit/tests/generator_test.php
+++ b/lib/phpunit/tests/generator_test.php
@@ -44,6 +44,11 @@ class core_phpunit_generator_testcase extends advanced_testcase {
         $count = $DB->count_records('user');
         $user = $generator->create_user();
         $this->assertEquals($count+1, $DB->count_records('user'));
+        $this->assertSame($user->username, clean_param($user->username, PARAM_USERNAME));
+        $this->assertSame($user->email, clean_param($user->email, PARAM_EMAIL));
+        $user = $generator->create_user(array('firstname'=>'Žluťoučký', 'lastname'=>'Koníček'));
+        $this->assertSame($user->username, clean_param($user->username, PARAM_USERNAME));
+        $this->assertSame($user->email, clean_param($user->email, PARAM_EMAIL));
 
         $count = $DB->count_records('course_categories');
         $category = $generator->create_category();