diff --git a/gtests/net/packetdrill/run_system_call.c b/gtests/net/packetdrill/run_system_call.c
index 017b7ee7baef599ebc8b858243e1d73ec38b524e..c161884a4eb9e36e8becb33fbe04b3656c6e308b 100644
--- a/gtests/net/packetdrill/run_system_call.c
+++ b/gtests/net/packetdrill/run_system_call.c
@@ -4303,7 +4303,7 @@ static int syscall_sctp_sendx(struct state *state, struct syscall_spec *syscall,
 	if (ellipsis_arg(args, 1, error))
 		return STATUS_ERR;
 	len_expr = get_arg(args, 2, error);
-	if (get_u32(len_expr, &len, error)) {
+	if (get_size_t(len_expr, &len, error)) {
 		 return STATUS_ERR;
 	}
 	addrs_expr = get_arg(args, 3, error);