diff --git a/dns/ddclient/src/opnsense/mvc/app/models/OPNsense/DynDNS/DynDNS.xml b/dns/ddclient/src/opnsense/mvc/app/models/OPNsense/DynDNS/DynDNS.xml
index c5521211f..df0a92297 100644
--- a/dns/ddclient/src/opnsense/mvc/app/models/OPNsense/DynDNS/DynDNS.xml
+++ b/dns/ddclient/src/opnsense/mvc/app/models/OPNsense/DynDNS/DynDNS.xml
@@ -69,7 +69,7 @@
                 </service>
                 <username type="TextField">
                     <Required>N</Required>
-                    <mask>/^([a-z0-9\-.@_:+])*$/u</mask>
+                    <mask>/^([a-zA-Z0-9\-.@_:+])*$/u</mask>
                     <ValidationMessage>The username contains invalid characters.</ValidationMessage>
                 </username>
                 <password type="UpdateOnlyTextField">