diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -2964,14 +2964,11 @@
 }
 
 int
-soshutdown(struct socket *so, int how)
+soshutdown(struct socket *so, enum shutdown_how how)
 {
 	struct protosw *pr;
 	int error, soerror_enotconn;
 
-	if (!(how == SHUT_RD || how == SHUT_WR || how == SHUT_RDWR))
-		return (EINVAL);
-
 	soerror_enotconn = 0;
 	SOCK_LOCK(so);
 	if ((so->so_state &
diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -1172,6 +1172,9 @@
 	struct file *fp;
 	int error;
 
+	if (__predict_false(how < SHUT_RD || how > SHUT_RDWR))
+		return (EINVAL);
+
 	AUDIT_ARG_FD(s);
 	error = getsock(td, s, &cap_shutdown_rights, &fp);
 	if (error == 0) {
diff --git a/sys/sys/socket.h b/sys/sys/socket.h
--- a/sys/sys/socket.h
+++ b/sys/sys/socket.h
@@ -627,9 +627,11 @@
 /*
  * howto arguments for shutdown(2), specified by Posix.1g.
  */
-#define	SHUT_RD		0		/* shut down the reading side */
-#define	SHUT_WR		1		/* shut down the writing side */
-#define	SHUT_RDWR	2		/* shut down both sides */
+enum shutdown_how {
+	SHUT_RD = 0,		/* shut down the reading side */
+	SHUT_WR,		/* shut down the writing side */
+	SHUT_RDWR		/* shut down both sides */
+};
 
 #if __BSD_VISIBLE
 /* for SCTP */
diff --git a/sys/sys/socketvar.h b/sys/sys/socketvar.h
--- a/sys/sys/socketvar.h
+++ b/sys/sys/socketvar.h
@@ -434,6 +434,7 @@
 struct sockaddr;
 struct ucred;
 struct uio;
+enum shutdown_how;
 
 /* Return values for socket upcalls. */
 #define	SU_OK		0
@@ -512,7 +513,7 @@
 int	sosend_generic(struct socket *so, struct sockaddr *addr,
 	    struct uio *uio, struct mbuf *top, struct mbuf *control,
 	    int flags, struct thread *td);
-int	soshutdown(struct socket *so, int how);
+int	soshutdown(struct socket *so, enum shutdown_how);
 void	soupcall_clear(struct socket *, sb_which);
 void	soupcall_set(struct socket *, sb_which, so_upcall_t, void *);
 void	solisten_upcall_set(struct socket *, so_upcall_t, void *);