diff --git a/core/modules/filter/filter.test b/core/modules/filter/filter.test
index a387f1f..bb8fc31 100644
--- a/core/modules/filter/filter.test
+++ b/core/modules/filter/filter.test
@@ -1214,6 +1214,11 @@ class FilterUnitTestCase extends DrupalUnitTestCase {
     // - absolute, mail, partial
     // - characters/encoding, surrounding markup, security
 
+    // Create a e-mail that is too long.
+    $long_email = str_repeat('a', 254) . '@example.com';
+    $too_long_email = str_repeat('b', 255) . '@example.com';
+
+
     // Filter selection/pattern matching.
     $tests = array(
       // HTTP URLs.
@@ -1225,10 +1230,12 @@ http://example.com or www.example.com
       ),
       // MAILTO URLs.
       '
-person@example.com or mailto:person2@example.com
+person@example.com or mailto:person2@example.com or ' . $long_email . ' but not ' . $too_long_email . '
 ' => array(
         '<a href="mailto:person@example.com">person@example.com</a>' => TRUE,
         '<a href="mailto:person2@example.com">mailto:person2@example.com</a>' => TRUE,
+        '<a href="mailto:' . $long_email . '">' . $long_email . '</a>' => TRUE,
+        '<a href="mailto:' . $too_long_email . '">' . $too_long_email . '</a>' => FALSE,
       ),
       // URI parts and special characters.
       '