diff --git a/include/rpc/xdr.h b/include/rpc/xdr.h
index 2ce9205422e..120925447d3 100644
--- a/include/rpc/xdr.h
+++ b/include/rpc/xdr.h
@@ -128,14 +128,14 @@ typedef struct __rpc_xdr {
  * The opaque pointer generally points to a structure of the data type
  * to be decoded.  If this pointer is 0, then the type routines should
  * allocate dynamic storage of the appropriate size and return it.
+ *
+ * Sometimes there is a third argument, sometimes not. So for correct
+ * prototyping, ... is required.
  */
 #ifdef _KERNEL
 typedef	bool_t (*xdrproc_t) __P((XDR *, void *, u_int));
 #else
-/*
- * XXX can't actually prototype it, because some take two args!!!
- */
-typedef	bool_t (*xdrproc_t) __P((/* XDR *, void *, u_int */));
+typedef	bool_t (*xdrproc_t) __P((XDR *, ...));
 #endif
 
 /*