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/common.test modules/simpletest/tests/common.test
index ca29e11..59d1def 100644
--- modules/simpletest/tests/common.test
+++ modules/simpletest/tests/common.test
@@ -2079,6 +2079,53 @@ class DrupalSystemListingTestCase extends DrupalWebTestCase {
   }
 }
 
+
+/**
+ * Tests for the drupal_get_path() function.
+ */
+class DrupalGetPathUnitTest extends DrupalWebTestCase {
+  public static function getInfo() {
+    return array(
+      'name' => 'Drupal get path',
+      'description' => 'Perform unit tests on the drupal_get_path() function.',
+      'group' => 'System',
+    );
+  }
+
+  /**
+   * Tests that drupal_get_path() function returns sensible results.
+   */
+  function testDrupalGetPath() {
+    $paths = array(
+      array(
+        'type' => 'theme',
+        'name' => 'test_theme',
+        'expected' => 'themes/tests/test_theme',
+      ),
+      array(
+        'type' => 'theme_engine',
+        'name' => 'phptemplate',
+        'expected' => 'themes/engines/phptemplate',
+      ),
+      array(
+        'type' => 'module',
+        'name' => 'simpletest',
+        'expected' => 'modules/simpletest',
+      ),
+      array(
+        'type' => 'profile',
+        'name' => 'standard',
+        'expected' => 'profiles/standard',
+      ),
+    );
+
+    foreach ($paths as $path) {
+      $this->assertEqual(drupal_get_path($path['type'], $path['name']), $path['expected'], t('Component @name of type @type was found at @path', array('@name' => $path['name'], '@type' => $path['type'], '@path' => $path['expected'])));
+    }
+
+  }
+}
+
 /**
  * Tests for the format_date() function.
  */