diff --git a/test-server/test-fraggle.c b/test-server/test-fraggle.c
index 2188799a..51b5903e 100644
--- a/test-server/test-fraggle.c
+++ b/test-server/test-fraggle.c
@@ -346,7 +346,8 @@ int main(int argc, char **argv)
 		struct lws_client_connect_info i;
 
 		address = argv[optind];
-		sprintf(ads_port, "%s:%u", address, port & 65535);
+		snprintf(ads_port, sizeof(ads_port), "%s:%u",
+			 address, port & 65535);
 		memset(&i, 0, sizeof(i));
 		i.context = context;
 		i.address = address;