diff --git a/modules/filter/filter.module b/modules/filter/filter.module
index 7c8b2b88cf..6c7707937a 100644
--- a/modules/filter/filter.module
+++ b/modules/filter/filter.module
@@ -1511,6 +1511,9 @@ function _filter_url($text, $filter) {
   $pattern = "`($url_pattern)($punctuation)`";
   $tasks['_filter_url_parse_partial_links'] = $pattern;
 
+  // Allow modules to alter the tasks and patterns.
+  drupal_alter('filter_url_tasks', $tasks);
+
   // Each type of URL needs to be processed separately. The text is joined and
   // re-split after each task, since all injected HTML tags must be correctly
   // protected before the next task.
diff --git a/modules/filter/filter.test b/modules/filter/filter.test
index 2af3103c12..96efe8442a 100644
--- a/modules/filter/filter.test
+++ b/modules/filter/filter.test
@@ -2043,3 +2043,50 @@ class FilterDOMSerializeTestCase extends DrupalWebTestCase {
     $this->assertEqual('', $result);
   }
 }
+
+/**
+ * Tests drupal_alter invocations in the filter module.
+ */
+class FilterDrupalAlterTestCase extends DrupalWebTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Filter drupal_alter',
+      'description' => 'Test drupal_alter invocations in the filter module.',
+      'group' => 'Filter',
+    );
+  }
+
+  function setUp() {
+    parent::setUp('filter_test');
+  }
+
+  /**
+   * Tests hook_filter_url_tasks_alter().
+   */
+  function testDrupalAlterFilterUrlTasks() {
+
+    // Setup dummy filter object.
+    $filter = new stdClass();
+    $filter->settings = array(
+      'filter_url_length' => 496,
+    );
+
+    $test_data = array(
+      '中文abc@example.com中文' => '<a href="mailto:中文abc@example.com中文">中文abc@example.com中文</a>',
+      '來信至xyz@來信至example.com' => '<a href="mailto:來信至xyz@來信至example.com">來信至xyz@來信至example.com</a>',
+    );
+
+    variable_set('drupal_alter_filter_url_tasks', FALSE);
+    foreach ($test_data as $filter_input => $expected_output) {
+      $filter_output = _filter_url($filter_input, $filter);
+      $this->assertNotEqual($filter_output, $expected_output, 'Filter did not produce expected results without drupal_alter.');
+    }
+
+    variable_set('drupal_alter_filter_url_tasks', TRUE);
+    foreach ($test_data as $filter_input => $expected_output) {
+      $filter_output = _filter_url($filter_input, $filter);
+      $this->assertEqual($filter_output, $expected_output, 'Filter produced expected results with drupal_alter.');
+    }
+  }
+}
diff --git a/modules/simpletest/tests/filter_test.module b/modules/simpletest/tests/filter_test.module
index 63b7f66d67..b0f1a153e6 100644
--- a/modules/simpletest/tests/filter_test.module
+++ b/modules/simpletest/tests/filter_test.module
@@ -62,3 +62,13 @@ function filter_test_replace($text, $filter, $format, $langcode, $cache, $cache_
   return implode("<br />\n", $text);
 }
 
+/**
+ * Implements hook_filter_url_tasks_alter().
+ */
+function filter_test_filter_url_tasks_alter(&$tasks) {
+  if (!variable_get('drupal_alter_filter_url_tasks', FALSE)) {
+    return;
+  }
+  // Alter the pattern for parsing email links to add the unicode modifier.
+  $tasks['_filter_url_parse_email_links'] = $tasks['_filter_url_parse_email_links'] . 'u';
+}