diff --git a/src/www/interfaces.php b/src/www/interfaces.php
index 67b344738..934dc7115 100644
--- a/src/www/interfaces.php
+++ b/src/www/interfaces.php
@@ -3023,9 +3023,9 @@ include("head.inc");
                                 $pconfig['track6-prefix-id'] = 0;
                             }
                             $track6_prefix_id_hex = !empty($pconfig['track6-prefix-id--hex']) ? $pconfig['track6-prefix-id--hex']: sprintf("%x", $pconfig['track6-prefix-id']);?>
-                            <div class="input-group">
+                            <div class="input-group" style="max-width:348px">
                               <div class="input-group-addon">0x</div>
-                              <input name="track6-prefix-id--hex" type="text" id="track6-prefix-id--hex" value="<?= $track6_prefix_id_hex ?>" />
+                              <input name="track6-prefix-id--hex" type="text" class="form-control" id="track6-prefix-id--hex" value="<?= $track6_prefix_id_hex ?>" />
                             </div>
                             <div class="hidden" data-for="help_for_track6-prefix-id">
                               <?= gettext('The value in this field is the delegated hexadecimal IPv6 prefix ID. This determines the configurable /64 network ID based on the dynamic IPv6 connection.') ?>