diff --git a/src/userfunc.c b/src/userfunc.c
index ffbbc2d..af1863f 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -480,7 +480,7 @@
 								  &argvars[i];
 	}
 
-	ret = call_func(name, len, rettv, argcount, argvars,
+	ret = call_func(name, len, rettv, argcount, argvars, NULL,
 		 firstline, lastline, doesrange, evaluate, partial, selfdict);
 
 	funcargs.ga_len -= i;
@@ -1139,7 +1139,7 @@
     }
 
     if (item == NULL)
-	r = call_func(name, (int)STRLEN(name), rettv, argc, argv,
+	r = call_func(name, (int)STRLEN(name), rettv, argc, argv, NULL,
 				 curwin->w_cursor.lnum, curwin->w_cursor.lnum,
 					     &dummy, TRUE, partial, selfdict);
 
@@ -1152,6 +1152,11 @@
 
 /*
  * Call a function with its resolved parameters
+ *
+ * "argv_func", when not NULL, can be used to fill in arguments only when the
+ * invoked function uses them.  It is called like this:
+ *   new_argcount = argv_func(current_argcount, argv, called_func_argcount)
+ *
  * Return FAIL when the function can't be called,  OK otherwise.
  * Also returns OK when an error was encountered while executing the function.
  */
@@ -1163,6 +1168,8 @@
     int		argcount_in,	/* number of "argvars" */
     typval_T	*argvars_in,	/* vars for arguments, must have "argcount"
 				   PLUS ONE elements! */
+    int		(* argv_func)(int, typval_T *, int),
+				/* function to fill in argvars */
     linenr_T	firstline,	/* first line of range */
     linenr_T	lastline,	/* last line of range */
     int		*doesrange,	/* return: function handled range */
@@ -1254,6 +1261,9 @@
 
 	    if (fp != NULL)
 	    {
+		if (argv_func != NULL)
+		    argcount = argv_func(argcount, argvars, fp->uf_args.ga_len);
+
 		if (fp->uf_flags & FC_RANGE)
 		    *doesrange = TRUE;
 		if (argcount < fp->uf_args.ga_len)