diff --git a/src/lib/gen/tcp_listen.c b/src/lib/gen/tcp_listen.c
index 093adcef..2b086035 100644
--- a/src/lib/gen/tcp_listen.c
+++ b/src/lib/gen/tcp_listen.c
@@ -160,6 +160,7 @@ tcp_listen(char *host, char *serv, size_t *addrlenp)
 static int
 cant_listen(char *host, char *serv, const char *err)
 {
-    fprintf(stderr, "Can't listen on %s:%s: %s\n", host, serv, err);
+    fprintf(stderr, "Can't listen on %s%s%s: %s\n",
+	    host ? host : "", host ? ":" : "", serv, err);
     exit(1);
 }