diff --git a/reference/stream/functions/stream-wrapper-register.xml b/reference/stream/functions/stream-wrapper-register.xml
index b6ecf95f65..24851ec448 100644
--- a/reference/stream/functions/stream-wrapper-register.xml
+++ b/reference/stream/functions/stream-wrapper-register.xml
@@ -29,6 +29,7 @@
      <listitem>
       <para>
        The wrapper name to be registered.
+       Valid protocol names must contain alphanumerics, dots (.), plusses (+), or hyphens (-) only.
       </para>
      </listitem>
     </varlistentry>