diff --git a/src/lib_table.c b/src/lib_table.c
index 8d53a6cd..542ed1f8 100644
--- a/src/lib_table.c
+++ b/src/lib_table.c
@@ -148,8 +148,8 @@ LJLIB_CF(table_concat)
   GCstr *sep = lj_lib_optstr(L, 2);
   MSize seplen = sep ? sep->len : 0;
   int32_t i = lj_lib_optint(L, 3, 1);
-  int32_t e = L->base+3 < L->top ? lj_lib_checkint(L, 4) :
-				   (int32_t)lj_tab_len(t);
+  int32_t e = (L->base+3 < L->top && !tvisnil(L->base+3)) ?
+	      lj_lib_checkint(L, 4) : (int32_t)lj_tab_len(t);
   luaL_buffinit(L, &b);
   if (i <= e) {
     for (;;) {