diff --git a/sys/rpc/auth_none.c b/sys/rpc/auth_none.c
--- a/sys/rpc/auth_none.c
+++ b/sys/rpc/auth_none.c
@@ -115,9 +115,7 @@
 	if (!XDR_PUTBYTES(xdrs, ap->mclient, ap->mcnt))
 		return (FALSE);
 
-	xdrmbuf_append(xdrs, args);
-
-	return (TRUE);
+	return (xdr_putmbuf(xdrs, args));
 }
 
 /* All these unused parameters are required to keep ANSI-C from grumbling */
diff --git a/sys/rpc/auth_unix.c b/sys/rpc/auth_unix.c
--- a/sys/rpc/auth_unix.c
+++ b/sys/rpc/auth_unix.c
@@ -251,9 +251,7 @@
 	if (!XDR_PUTBYTES(xdrs, au->au_marshed, au->au_mpos))
 		return (FALSE);
 
-	xdrmbuf_append(xdrs, args);
-
-	return (TRUE);
+	return (xdr_putmbuf(xdrs, args));
 }
 
 static bool_t
diff --git a/sys/rpc/rpcsec_gss/rpcsec_gss.c b/sys/rpc/rpcsec_gss/rpcsec_gss.c
--- a/sys/rpc/rpcsec_gss/rpcsec_gss.c
+++ b/sys/rpc/rpcsec_gss/rpcsec_gss.c
@@ -547,8 +547,7 @@
 			_rpc_gss_set_error(RPC_GSS_ER_SYSTEMERROR, ENOMEM);
 			return (FALSE);
 		}
-		xdrmbuf_append(xdrs, args);
-		return (TRUE);
+		return (xdr_putmbuf(xdrs, args));
 	} else {
 		/*
 		 * Keep track of this XID + seq pair so that we can do
@@ -596,15 +595,13 @@
 		}
 		if (gd->gd_state != RPCSEC_GSS_ESTABLISHED ||
 		    gd->gd_cred.gc_svc == rpc_gss_svc_none) {
-			xdrmbuf_append(xdrs, args);
-			return (TRUE);
+			return (xdr_putmbuf(xdrs, args));
 		} else {
 			if (!xdr_rpc_gss_wrap_data(&args,
 				gd->gd_ctx, gd->gd_qop, gd->gd_cred.gc_svc,
 				seq))
 				return (FALSE);
-			xdrmbuf_append(xdrs, args);
-			return (TRUE);
+			return (xdr_putmbuf(xdrs, args));
 		}
 	}
 
diff --git a/sys/rpc/rpcsec_tls/auth_tls.c b/sys/rpc/rpcsec_tls/auth_tls.c
--- a/sys/rpc/rpcsec_tls/auth_tls.c
+++ b/sys/rpc/rpcsec_tls/auth_tls.c
@@ -124,9 +124,7 @@
 	if (!XDR_PUTBYTES(xdrs, ap->mclient, ap->mcnt))
 		return (FALSE);
 
-	xdrmbuf_append(xdrs, args);
-
-	return (TRUE);
+	return (xdr_putmbuf(xdrs, args));
 }
 
 /* All these unused parameters are required to keep ANSI-C from grumbling */
diff --git a/sys/rpc/svc_dg.c b/sys/rpc/svc_dg.c
--- a/sys/rpc/svc_dg.c
+++ b/sys/rpc/svc_dg.c
@@ -240,7 +240,7 @@
 		if (!xdr_replymsg(&xdrs, msg))
 			stat = FALSE;
 		else
-			xdrmbuf_append(&xdrs, m);
+			(void)xdr_putmbuf(&xdrs, m);
 	} else {
 		stat = xdr_replymsg(&xdrs, msg);
 	}
diff --git a/sys/rpc/svc_vc.c b/sys/rpc/svc_vc.c
--- a/sys/rpc/svc_vc.c
+++ b/sys/rpc/svc_vc.c
@@ -1001,7 +1001,7 @@
 		if (!xdr_replymsg(&xdrs, msg))
 			stat = FALSE;
 		else
-			xdrmbuf_append(&xdrs, m);
+			(void)xdr_putmbuf(&xdrs, m);
 	} else {
 		stat = xdr_replymsg(&xdrs, msg);
 	}
@@ -1085,7 +1085,7 @@
 		if (!xdr_replymsg(&xdrs, msg))
 			stat = FALSE;
 		else
-			xdrmbuf_append(&xdrs, m);
+			(void)xdr_putmbuf(&xdrs, m);
 	} else {
 		stat = xdr_replymsg(&xdrs, msg);
 	}
diff --git a/sys/rpc/xdr.h b/sys/rpc/xdr.h
--- a/sys/rpc/xdr.h
+++ b/sys/rpc/xdr.h
@@ -40,6 +40,8 @@
 #define _KRPC_XDR_H
 #include <sys/cdefs.h>
 
+struct mbuf;
+
 /*
  * XDR provides a conventional way for converting between C data
  * types and an external bit-string representation.  Library supplied
@@ -105,6 +107,8 @@
 		bool_t	(*x_getbytes)(struct XDR *, char *, u_int);
 		/* put some bytes to " */
 		bool_t	(*x_putbytes)(struct XDR *, const char *, u_int);
+		/* put mbuf or copy its bytes */
+		bool_t	(*x_putmbuf)(struct XDR *, struct mbuf *);
 		/* returns bytes off from beginning */
 		u_int	(*x_getpostn)(struct XDR *);
 		/* lets you reposition the stream */
@@ -190,6 +194,11 @@
 #define xdr_putbytes(xdrs, addr, len)			\
 	(*(xdrs)->x_ops->x_putbytes)(xdrs, addr, len)
 
+#define XDR_PUTMBUF(xdrs, mbuf)				\
+	(*(xdrs)->x_ops->x_putmbuf)(xdrs, mbuf)
+#define xdr_putmbuf(xdrs, mbuf)				\
+	(*(xdrs)->x_ops->x_putmbuf)(xdrs, mbuf)
+
 #define XDR_GETPOS(xdrs)				\
 	(*(xdrs)->x_ops->x_getpostn)(xdrs)
 #define xdr_getpos(xdrs)				\
@@ -359,9 +368,7 @@
 extern void   xdrmem_create(XDR *, char *, u_int, enum xdr_op);
 
 /* XDR using mbufs */
-struct mbuf;
 extern void   xdrmbuf_create(XDR *, struct mbuf *, enum xdr_op);
-extern void   xdrmbuf_append(XDR *, struct mbuf *);
 extern struct mbuf * xdrmbuf_getall(XDR *);
 
 /* XDR pseudo records for tcp */
diff --git a/sys/xdr/xdr_mbuf.c b/sys/xdr/xdr_mbuf.c
--- a/sys/xdr/xdr_mbuf.c
+++ b/sys/xdr/xdr_mbuf.c
@@ -40,6 +40,7 @@
 static bool_t xdrmbuf_putlong(XDR *, const long *);
 static bool_t xdrmbuf_getbytes(XDR *, char *, u_int);
 static bool_t xdrmbuf_putbytes(XDR *, const char *, u_int);
+static bool_t xdrmbuf_putmbuf(XDR *, struct mbuf *);
 /* XXX: w/64-bit pointers, u_int not enough! */
 static u_int xdrmbuf_getpos(XDR *);
 static bool_t xdrmbuf_setpos(XDR *, u_int);
@@ -50,6 +51,7 @@
 	.x_putlong =	xdrmbuf_putlong,
 	.x_getbytes =	xdrmbuf_getbytes,
 	.x_putbytes =	xdrmbuf_putbytes,
+	.x_putmbuf =	xdrmbuf_putmbuf,
 	.x_getpostn =	xdrmbuf_getpos,
 	.x_setpostn =	xdrmbuf_setpos,
 	.x_inline =	xdrmbuf_inline,
@@ -78,17 +80,17 @@
 	}
 }
 
-void
-xdrmbuf_append(XDR *xdrs, struct mbuf *madd)
+/*
+ * Append mbuf.  Always succeds and we own mbuf.
+ */
+static bool_t
+xdrmbuf_putmbuf(XDR *xdrs, struct mbuf *madd)
 {
 	struct mbuf *m;
 
-	KASSERT(xdrs->x_ops == &xdrmbuf_ops && xdrs->x_op == XDR_ENCODE,
-	    ("xdrmbuf_append: invalid XDR stream"));
-
 	if (m_length(madd, NULL) == 0) {
 		m_freem(madd);
-		return;
+		return (TRUE);
 	}
 
 	m = (struct mbuf *) xdrs->x_private;
@@ -97,6 +99,8 @@
 	m = m_last(madd);
 	xdrs->x_private = m;
 	xdrs->x_handy = m->m_len;
+
+	return (TRUE);
 }
 
 struct mbuf *