diff --git a/lib/libnetmap/nmreq.c b/lib/libnetmap/nmreq.c
--- a/lib/libnetmap/nmreq.c
+++ b/lib/libnetmap/nmreq.c
@@ -54,8 +54,15 @@
 nm_is_identifier(const char *s, const char *e)
 {
 	for (; s != e; s++) {
-		if (!isalnum(*s) && *s != '_') {
+		switch (*s) {
+		case '^': /* only SW ring */
+		case '*': /* NIC and SW */
+		case '-': /* one NIC ring pair */
+		case '/': /* start of flags */
+		case '@': /* start of memid */
 			return 0;
+		default:
+			break;
 		}
 	}