diff --git a/src/lj_opt_narrow.c b/src/lj_opt_narrow.c
index 34fe6c39..70686681 100644
--- a/src/lj_opt_narrow.c
+++ b/src/lj_opt_narrow.c
@@ -501,7 +501,8 @@ TRef LJ_FASTCALL lj_opt_narrow_cindex(jit_State *J, TRef tr)
 {
   lua_assert(tref_isnumber(tr));
   if (tref_isnum(tr))
-    return emitir(IRT(IR_CONV, IRT_INTP), tr, (IRT_INTP<<5)|IRT_NUM|IRCONV_ANY);
+    return emitir(IRT(IR_CONV, IRT_INTP), tr,
+            (IRT_INTP<<5)|IRT_NUM|IRCONV_TRUNC|IRCONV_ANY);
   /* Undefined overflow semantics allow stripping of ADDOV, SUBOV and MULOV. */
   return narrow_stripov(J, tr, IR_MULOV,
 			LJ_64 ? ((IRT_INTP<<5)|IRT_INT|IRCONV_SEXT) :