1 files changed, 4 insertions, 1 deletions

diff --git a/src/lj_strfmt.c b/src/lj_strfmt.c
index 7b073470..945954aa 100644
--- a/src/lj_strfmt.c
+++ b/src/lj_strfmt.c
@@ -431,7 +431,7 @@ int lj_strfmt_putarg(lua_State *L, SBuf *sb, int arg, int retry)
         MSize len;
         const char *s;
         cTValue *mo;
-        if (LJ_UNLIKELY(!tvisstr(o)) && retry >= 0 &&
+        if (LJ_UNLIKELY(!tvisstr(o) && !tvisbuf(o)) && retry >= 0 &&
             !tvisnil(mo = lj_meta_lookup(L, o, MM_tostring))) {
           /* Call __tostring metamethod once. */
           copyTV(L, L->top++, mo);
@@ -447,10 +447,13 @@ int lj_strfmt_putarg(lua_State *L, SBuf *sb, int arg, int retry)
         if (LJ_LIKELY(tvisstr(o))) {
           len = strV(o)->len;
           s = strVdata(o);
+#if LJ_HASBUFFER
         } else if (tvisbuf(o)) {
           SBufExt *sbx = bufV(o);
+          if (sbx == (SBufExt *)sb) lj_err_arg(L, arg+1, LJ_ERR_BUFFER_SELF);
           len = sbufxlen(sbx);
           s = sbx->r;
+#endif
         } else {
           GCstr *str = lj_strfmt_obj(L, o);
           len = str->len;