diff --git a/src/lj_serialize.c b/src/lj_serialize.c
index ae35a6dd..be09d670 100644
--- a/src/lj_serialize.c
+++ b/src/lj_serialize.c
@@ -224,11 +224,13 @@ static char *serialize_put(char *w, StrBuf *sbuf, cTValue *o)
       ud = lj_bswap(ud);
 #endif
       *w++ = SER_TAG_LIGHTUD32; memcpy(w, &ud, 4); w += 4;
+#if LJ_64
     } else {
 #if LJ_BE
       ud = lj_bswap64(ud);
 #endif
       *w++ = SER_TAG_LIGHTUD64; memcpy(w, &ud, 8); w += 8;
+#endif
     }
   } else {
     /* NYI userdata */