diff --git includes/bootstrap.inc includes/bootstrap.inc
index be0a471..b47ac36 100644
--- includes/bootstrap.inc
+++ includes/bootstrap.inc
@@ -677,7 +677,7 @@ function drupal_get_filename($type, $name, $filename = NULL) {
     try {
       if (function_exists('db_query')) {
         $file = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
-        if (file_exists(DRUPAL_ROOT . '/' . $file)) {
+        if (!empty($file) && file_exists(DRUPAL_ROOT . '/' . $file)) {
           $files[$type][$name] = $file;
         }
       }
diff --git modules/simpletest/tests/bootstrap.test modules/simpletest/tests/bootstrap.test
index 333f34b..c7774aa 100644
--- modules/simpletest/tests/bootstrap.test
+++ modules/simpletest/tests/bootstrap.test
@@ -324,7 +324,7 @@ class HookBootExitTestCase extends DrupalWebTestCase {
 /**
  * Test drupal_get_filename()'s availability.
  */
-class BootstrapGetFilenameTestCase extends DrupalUnitTestCase {
+class BootstrapGetFilenameTestCase extends DrupalWebTestCase {
 
   public static function getInfo() {
     return array(
@@ -497,4 +497,3 @@ class BootstrapOverrideServerVariablesTestCase extends DrupalUnitTestCase {
     }
   }
 }
-