Index: head/lib/libc/gen/getpeereid.c
===================================================================
--- head/lib/libc/gen/getpeereid.c
+++ head/lib/libc/gen/getpeereid.c
@@ -47,7 +47,7 @@
 	int error;
 
 	xuclen = sizeof(xuc);
-	error = _getsockopt(s, 0, LOCAL_PEERCRED, &xuc, &xuclen);
+	error = _getsockopt(s, SOL_LOCAL, LOCAL_PEERCRED, &xuc, &xuclen);
 	if (error != 0)
 		return (error);
 	if (xuc.cr_version != XUCRED_VERSION) {
Index: head/share/man/man4/unix.4
===================================================================
--- head/share/man/man4/unix.4
+++ head/share/man/man4/unix.4
@@ -28,7 +28,7 @@
 .\"     @(#)unix.4	8.1 (Berkeley) 6/9/93
 .\" $FreeBSD$
 .\"
-.Dd August 19, 2018
+.Dd August 3, 2020
 .Dt UNIX 4
 .Os
 .Sh NAME
@@ -195,7 +195,9 @@
 reused for a new process.
 .Sh SOCKET OPTIONS
 .Tn UNIX
-domain sockets support a number of socket options which can be set with
+domain sockets support a number of socket options for the options level
+.Dv SOL_LOCAL ,
+which can be set with
 .Xr setsockopt 2
 and tested with
 .Xr getsockopt 2 :
Index: head/sys/kern/uipc_usrreq.c
===================================================================
--- head/sys/kern/uipc_usrreq.c
+++ head/sys/kern/uipc_usrreq.c
@@ -1470,7 +1470,7 @@
 	struct xucred xu;
 	int error, optval;
 
-	if (sopt->sopt_level != 0)
+	if (sopt->sopt_level != SOL_LOCAL)
 		return (EINVAL);
 
 	unp = sotounpcb(so);
Index: head/sys/sys/un.h
===================================================================
--- head/sys/sys/un.h
+++ head/sys/sys/un.h
@@ -62,6 +62,8 @@
 
 #if __BSD_VISIBLE
 
+#define	SOL_LOCAL		0	/* Options for local socket */
+
 /* Socket options. */
 #define	LOCAL_PEERCRED		1	/* retrieve peer credentials */
 #define	LOCAL_CREDS		2	/* pass credentials to receiver */