diff --git a/sys/amd64/cloudabi64/cloudabi64_sysvec.c b/sys/amd64/cloudabi64/cloudabi64_sysvec.c
index f0aeb2e7b63a..08d85a2d5cb7 100644
--- a/sys/amd64/cloudabi64/cloudabi64_sysvec.c
+++ b/sys/amd64/cloudabi64/cloudabi64_sysvec.c
@@ -96,6 +96,7 @@ cloudabi64_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
 	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;
diff --git a/sys/arm64/cloudabi64/cloudabi64_sysvec.c b/sys/arm64/cloudabi64/cloudabi64_sysvec.c
index 913d1278ffd3..cf3e594244bb 100644
--- a/sys/arm64/cloudabi64/cloudabi64_sysvec.c
+++ b/sys/arm64/cloudabi64/cloudabi64_sysvec.c
@@ -77,6 +77,7 @@ cloudabi64_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
 	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++)