diff --git a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php b/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
index b59b130f09..71532f4e92 100644
--- a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
+++ b/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
@@ -73,7 +73,7 @@ class AphrontDefaultApplicationConfiguration
         'edit/(?:(?P<id>\d+)/(?:(?P<view>\w+)/)?)?'
           => 'PhabricatorPeopleEditController',
       ),
-      '/p/(?P<username>\w+)/(?:(?P<page>\w+)/)?'
+      '/p/(?P<username>[\w._-]+)/(?:(?P<page>\w+)/)?'
         => 'PhabricatorPeopleProfileController',
       '/conduit/' => array(
         '' => 'PhabricatorConduitListController',
diff --git a/src/applications/people/storage/PhabricatorUser.php b/src/applications/people/storage/PhabricatorUser.php
index 93c19b701d..3f54a6efe3 100644
--- a/src/applications/people/storage/PhabricatorUser.php
+++ b/src/applications/people/storage/PhabricatorUser.php
@@ -595,6 +595,13 @@ EOBODY;
   }
 
   public static function validateUsername($username) {
+    // NOTE: If you update this, make sure to update:
+    //
+    //  - Remarkup rule for @mentions.
+    //  - Routing rule for "/p/username/".
+    //  - Unit tests, obviously.
+    //  - describeValidUsername() method, above.
+
     return (bool)preg_match('/^[a-zA-Z0-9._-]*[a-zA-Z0-9_-]$/', $username);
   }