--- sys/amd64/cloudabi64/cloudabi64_sysvec.c	(revision 302343)
+++ sys/amd64/cloudabi64/cloudabi64_sysvec.c	(working copy)
@@ -96,6 +96,7 @@ 
 	if (sa->code >= CLOUDABI64_SYS_MAXSYSCALL)
 		return (ENOSYS);
 	sa->callp = &cloudabi64_sysent[sa->code];
+	sa->narg = sa->callp->sy_narg;
 
 	/* Fetch system call arguments. */
 	sa->args[0] = frame->tf_rdi;
--- sys/arm64/cloudabi64/cloudabi64_sysvec.c	(revision 302343)
+++ sys/arm64/cloudabi64/cloudabi64_sysvec.c	(working copy)
@@ -77,6 +77,7 @@ 
 	if (sa->code >= CLOUDABI64_SYS_MAXSYSCALL)
 		return (ENOSYS);
 	sa->callp = &cloudabi64_sysent[sa->code];
+	sa->narg = sa->callp->sy_narg;
 
 	/* Fetch system call arguments. */
 	for (i = 0; i < MAXARGS; i++)