diff --git a/tools/testing/selftests/net/cmsg_sender.c b/tools/testing/selftests/net/cmsg_sender.c
index 75dd83e39207bd38d6943c4eff5d155c005e12d3..24b21b15ed3fb05ba677328c4d68a258d9819169 100644
--- a/tools/testing/selftests/net/cmsg_sender.c
+++ b/tools/testing/selftests/net/cmsg_sender.c
@@ -110,7 +110,7 @@ static void __attribute__((noreturn)) cs_usage(const char *bin)
 
 static void cs_parse_args(int argc, char *argv[])
 {
-	char o;
+	int o;
 
 	while ((o = getopt(argc, argv, "46sS:p:m:M:d:tf:F:c:C:l:L:H:")) != -1) {
 		switch (o) {