diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c
index 5e222ba977e4..3b8d2c8a6216 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_diag.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c
@@ -377,7 +377,8 @@ static void get_subflow_info(char *subflow_addrs)
 	int ret;
 	int fd;
 
-	ret = sscanf(subflow_addrs, "%[^:]:%d %[^:]:%d", saddr, &sport, daddr, &dport);
+	ret = sscanf(subflow_addrs, "%63[^:]:%d %63[^:]:%d",
+		     saddr, &sport, daddr, &dport);
 	if (ret != 4)
 		die_perror("IP PORT Pairs has style problems!");