--- a/vpn/openconnect/openconnectauth.cpp
+++ b/vpn/openconnect/openconnectauth.cpp
@@ -214,10 +214,12 @@ void OpenconnectAuthWidget::readConfig()
             openconnect_passphrase_from_fsid(d->vpninfo);
         }
     }
+#if OPENCONNECT_CHECK_VER(5,2)
     if (!dataMap[NM_OPENCONNECT_KEY_PROTOCOL].isEmpty()) {
         const QString protocol = dataMap[NM_OPENCONNECT_KEY_PROTOCOL];
         openconnect_set_protocol(d->vpninfo, OC3DUP(protocol == "juniper" ? "nc" : protocol.toUtf8().data()));
     }
+#endif
     if (!dataMap[NM_OPENCONNECT_KEY_REPORTED_OS].isEmpty()) {
         const QString reportedOs = dataMap[NM_OPENCONNECT_KEY_REPORTED_OS];
         openconnect_set_reported_os(d->vpninfo, reportedOs.toUtf8().data());