diff --git a/kamailio/registrar-role.cfg b/kamailio/registrar-role.cfg
index b1ffeaf..1da60da 100644
--- a/kamailio/registrar-role.cfg
+++ b/kamailio/registrar-role.cfg
@@ -136,7 +136,7 @@ route[ATTEMPT_AUTHORIZATION]
     if(@contact.expires) {
         $var(expires) = @contact.expires;
     } else { 
-        if($hdr(Expires)) {
+        if(is_present_hf("Expires")) {
            $var(expires) = $hdr(Expires);
         } else {
            $var(expires) = REGISTRAR_MIN_EXPIRES;