diff --git a/test/Makefile b/test/Makefile
index 08f0c2d..91498ff 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -63,7 +63,7 @@ LOCAL_ASSETS = mbuto.img QEMU_EFI.fd \
 
 ASSETS = $(DOWNLOAD_ASSETS) $(LOCAL_ASSETS)
 
-CFLAGS = -Wall -Werror
+CFLAGS = -Wall -Werror -Wextra -pedantic -std=c99
 
 assets: $(ASSETS)
 
diff --git a/test/nsholder.c b/test/nsholder.c
index aac901b..010a051 100644
--- a/test/nsholder.c
+++ b/test/nsholder.c
@@ -53,7 +53,7 @@ static void hold(int fd, const struct sockaddr_un *addr)
 	if (rc < 0)
 		die("listen(): %s\n", strerror(errno));
 
-	printf("nsholder: local PID=%d  local UID=%d  local GID=%d\n",
+	printf("nsholder: local PID=%d  local UID=%u  local GID=%u\n",
 	       getpid(), getuid(), getgid());
 	do {
 		int afd = accept(fd, NULL, NULL);