diff -Naur samba-4.11.0/source3/winbindd/winbindd_util.c samba-4.11.0-fix-winbind_local_user_no_domain/source3/winbindd/winbindd_util.c
--- samba-4.11.0/source3/winbindd/winbindd_util.c	2019-02-21 07:53:38.372548632 -0500
+++ samba-4.11.0-fix-winbind_local_user_no_domain/source3/winbindd/winbindd_util.c	2019-03-02 16:27:31.126990704 -0500
@@ -1607,7 +1607,8 @@
 			fstrcpy(domain, lp_workgroup());
 			fstrcpy(namespace, domain);
 		} else {
-			fstrcpy(namespace, lp_netbios_name());
+                        /* local user and winbind_use_default_domain not set */
+			return false;
 		}
 	}