diff --git a/src/lj_load.c b/src/lj_load.c
index 828bf8ae..24b660a8 100644
--- a/src/lj_load.c
+++ b/src/lj_load.c
@@ -122,8 +122,9 @@ LUALIB_API int luaL_loadfilex(lua_State *L, const char *filename,
     copyTV(L, L->top-1, L->top);
   }
   if (err) {
+    const char *fname = filename ? filename : "stdin";
     L->top--;
-    lua_pushfstring(L, "cannot read %s: %s", chunkname+1, strerror(err));
+    lua_pushfstring(L, "cannot read %s: %s", fname, strerror(err));
     return LUA_ERRFILE;
   }
   return status;
diff --git a/src/lj_record.c b/src/lj_record.c
index c6a082d4..ad45bebb 100644
--- a/src/lj_record.c
+++ b/src/lj_record.c
@@ -1107,7 +1107,10 @@ int lj_record_mm_lookup(jit_State *J, RecordIndex *ix, MMS mm)
       return 0;  /* No metamethod. */
     }
     /* The cdata metatable is treated as immutable. */
-    if (LJ_HASFFI && tref_iscdata(ix->tab)) goto immutable_mt;
+    if (LJ_HASFFI && tref_iscdata(ix->tab)) {
+      mix.tab = TREF_NIL;
+      goto immutable_mt;
+    }
     ix->mt = mix.tab = lj_ir_ggfload(J, IRT_TAB,
       GG_OFS(g.gcroot[GCROOT_BASEMT+itypemap(&ix->tabv)]));
     goto nocheck;