1 files changed, 1 insertions, 1 deletions

diff --git a/core.c b/core.c
index 0bffb92..7a14408 100644
--- a/core.c
+++ b/core.c
@@ -10,7 +10,7 @@
 static int
 lua_isatty(lua_State *L)
 {
-    FILE **fp = (FILE **) luaL_checkudata(L, -1, LUA_FILEHANDLE);
+    FILE **fp = (FILE **) luaL_checkudata(L, 1, LUA_FILEHANDLE);
 
     lua_pushboolean(L, isatty(fileno(*fp)));
     return 1;