1 files changed, 2 insertions, 2 deletions

diff --git a/src/lib_table.c b/src/lib_table.c
index 4f5d9d0d..80c7c8dc 100644
--- a/src/lib_table.c
+++ b/src/lib_table.c
@@ -134,8 +134,8 @@ LJLIB_CF(table_concat)		LJLIB_REC(.)
   GCtab *t = lj_lib_checktab(L, 1);
   GCstr *sep = lj_lib_optstr(L, 2);
   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);
   SBuf *sb = lj_buf_tmp_(L);
   SBuf *sbx = lj_buf_puttab(sb, t, sep, i, e);
   if (LJ_UNLIKELY(!sbx)) {  /* Error: bad element type. */