diff --git a/opt/plan9-opcodes.c b/opt/plan9-opcodes.c
index aa29df1a..d4ef0220 100644
--- a/opt/plan9-opcodes.c
+++ b/opt/plan9-opcodes.c
@@ -15,5 +15,5 @@ _FN1(_I(SEXP_STRING), _I(SEXP_STRING), "getenv", 0, sexp_getenv),
 _FN1(_I(SEXP_FIXNUM), _I(SEXP_STRING), "change-directory", 0, sexp_chdir),
 _FN0(_I(SEXP_FIXNUM), "wait", 0, sexp_wait),
 _FN2(_I(SEXP_FIXNUM), _I(SEXP_FIXNUM), _I(SEXP_STRING), "post-note", 0, sexp_postnote),
-_FN4(_I(SEXP_FIXNUM), _I(SEXP_PAIR), _I(SEXP_STRING), "%postmountsrv", 0, sexp_postmountsrv),
+_FN4(_I(SEXP_FIXNUM), _I(SEXP_PAIR), _I(SEXP_STRING), _I(SEXP_STRING), "%postmountsrv", 0, sexp_postmountsrv),
 _FN1(_I(SEXP_FIXNUM), _I(SEXP_STRING), "file-exists?", 0, sexp_file_exists_p),