diff -ru samba-3.5.5.orig/source3/libsmb/namequery_dc.c samba-3.5.5/source3/libsmb/namequery_dc.c
--- samba-3.5.5.orig/source3/libsmb/namequery_dc.c	2010-09-09 07:22:50.000000000 -0700
+++ samba-3.5.5/source3/libsmb/namequery_dc.c	2010-09-25 06:56:59.000000000 -0700
@@ -233,13 +233,9 @@
 		ret = ads_dc_name(domain, realm, &dc_ss, srv_name);
 	}
 
-	if (!domain) {
-		/* if we have only the realm we can't do anything else */
-		return False;
-	}
-
-	if (!ret) {
-		/* fall back on rpc methods if the ADS methods fail */
+	if (!ret && (domain && *domain)) {
+		/* fall back on rpc methods if the ADS methods fail,
+		   but only if we know the domain name */
 		ret = rpc_dc_name(domain, srv_name, &dc_ss);
 	}