diff --git a/docs/configuration.md b/docs/configuration.md
index ab475e382..ca04dbc7b 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -1096,7 +1096,8 @@ setting the ASN (archive serial number) if a properly formatted
 barcode is detected.
 
     The barcode must consist of a (configurable) prefix and the ASN
-    to be set, for instance `ASN00123`.
+    to be set, for instance `ASN00123`. The content after the prefix
+    is cleaned of non-numeric characters.
 
     This option is compatible with barcode page separation, since
     pages will be split up before reading the ASN.