1 files changed, 9 insertions, 1 deletions
diff --git a/src/algo.h b/src/algo.h
index 2255070..5d25330 100644
--- a/src/algo.h
+++ b/src/algo.h
@@ -119,8 +119,13 @@ static void check_subject (lua_State *L, int pos, TArgExec *argE)
   int stype;
   argE->text = lua_tolstring (L, pos, &argE->textlen);
   stype = lua_type (L, pos);
+#if LUA_VERSION_NUM == 501
+  if (stype != LUA_TSTRING && stype != LUA_TUSERDATA) {
+    luaL_typerror (L, pos, "string or userdata");
+#else
   if (stype != LUA_TSTRING && stype != LUA_TTABLE && stype != LUA_TUSERDATA) {
     luaL_typerror (L, pos, "string, table or userdata");
+#endif
   } else if (argE->text == NULL) {
     int type;
     lua_getfield (L, pos, "topointer");
@@ -135,7 +140,10 @@ static void check_subject (lua_State *L, int pos, TArgExec *argE)
     argE->text = lua_touserdata (L, -1);
     lua_pop (L, 1);
 #if LUA_VERSION_NUM == 501
-    lua_objlen (L, pos);
+    if (!luaL_getmetafield (L, pos, "__len") || lua_type (L, -1) != LUA_TFUNCTION)
+      luaL_argerror (L, pos, "the userdata has no valid __len metafield");
+    lua_pushvalue (L, pos);
+    lua_call (L, 1, 1);
 #else
     lua_len (L, pos);
 #endif