diff --git a/OpenKeychain/src/main/res/xml/usb_device_filter.xml b/OpenKeychain/src/main/res/xml/usb_device_filter.xml
index 4686b6da9..294b83659 100644
--- a/OpenKeychain/src/main/res/xml/usb_device_filter.xml
+++ b/OpenKeychain/src/main/res/xml/usb_device_filter.xml
@@ -4,6 +4,7 @@
     <!--
         Route all smart card devices (class 11) to OpenKeychain.
         Internally, we check against a whitelist of working devices.
+        See SecurityTokenInfo.
     -->
     <usb-device class="11" />