diff --git a/src/lj_opt_narrow.c b/src/lj_opt_narrow.c
index 37fda0b6..d9d1e2ba 100644
--- a/src/lj_opt_narrow.c
+++ b/src/lj_opt_narrow.c
@@ -284,7 +284,8 @@ static int narrow_conv_backprop(NarrowConv *nc, IRRef ref, int depth)
       }
     } else {
       int32_t k = lj_num2int(n);
-      if (n == (lua_Number)k) {  /* Only if constant is really an integer. */
+      /* Only if constant is a small integer. */
+      if (checki16(k) && n == (lua_Number)k) {
 	*nc->sp++ = NARROWINS(NARROW_INT, 0);
 	*nc->sp++ = (NarrowIns)k;
 	return 0;