diff --git a/luprex/cpp/core/luastack.hpp b/luprex/cpp/core/luastack.hpp
index f6c2fd70..1cb3ab44 100644
--- a/luprex/cpp/core/luastack.hpp
+++ b/luprex/cpp/core/luastack.hpp
@@ -147,6 +147,7 @@
 #include "wrap-set.hpp"
 #include <cstring>
 #include <type_traits>
+#include <cassert>
 
 #include "lua.h"
 #include "lauxlib.h"
@@ -296,34 +297,45 @@ protected:
         int nvar;
         int nextra;
         constexpr Counts(int nr, int na, int nv, int ne) : nret(nr), narg(na), nvar(nv), nextra(ne) {}
+		constexpr Counts(Counts a, Counts b)
+			: nret(a.nret+b.nret), narg(a.narg+b.narg), nvar(a.nvar+b.nvar), nextra(a.nextra+b.nextra) {}
     };
 
-    template<int NRET, int NARG, int NVAR, int NEXTRA, class... SS>
-    constexpr static Counts count_slots(LuaRet &v, SS & ... stackslots)
+    template<class... SS>
+    constexpr static Counts count_slots(LuaRet &v, SS && ... stackslots)
     {
-        return count_slots<NRET+1, NARG, NVAR, NEXTRA>(stackslots...);
+        return Counts(Counts(1, 0, 0, 0), count_slots(stackslots...));
     }
-    template<int NRET, int NARG, int NVAR, int NEXTRA, class... SS>
-    constexpr static Counts count_slots(LuaArg &v, SS & ... stackslots)
+    template<class... SS>
+    constexpr static Counts count_slots(LuaArg &v, SS && ... stackslots)
     {
-        return count_slots<NRET, NARG+1, NVAR, NEXTRA>(stackslots...);
+        return Counts(Counts(0, 1, 0, 0), count_slots(stackslots...));
     }
-    template<int NRET, int NARG, int NVAR, int NEXTRA, class... SS>
-    constexpr static Counts count_slots(LuaVar &v, SS & ... stackslots)
+    template<class... SS>
+    constexpr static Counts count_slots(LuaVar &v, SS && ... stackslots)
     {
-        return count_slots<NRET, NARG, NVAR+1, NEXTRA>(stackslots...);
+        return Counts(Counts(0, 0, 1, 0), count_slots(stackslots...));
     }
-    template<int NRET, int NARG, int NVAR, int NEXTRA, class... SS>
-    constexpr static Counts count_slots(LuaExtraArgs &v, SS & ... stackslots)
+    template<class... SS>
+    constexpr static Counts count_slots(LuaExtraArgs &v, SS && ... stackslots)
     {
-        return count_slots<NRET, NARG, NVAR, NEXTRA+1>(stackslots...);
+        return Counts(Counts(0, 0, 0, 1), count_slots(stackslots...));
     }
-    template<int NRET, int NARG, int NVAR, int NEXTRA>
     constexpr static Counts count_slots() {
-        return Counts(NRET, NARG, NVAR, NEXTRA);
+        return Counts(0, 0, 0, 0);
     }
 
-private:
+
+    template<class... SS>
+    constexpr static int count_vars(LuaVar &v, SS && ... stackslots)
+    {
+        return 1 + count_vars(stackslots...);
+    }
+    constexpr static int count_vars() {
+        return 0;
+    }
+
+    private:
     // Push any value on the stack, by type.
     void push_any_value(LuaNewTableMarker s) const { lua_newtable(L_); }
     void push_any_value(LuaNilMarker s) const { lua_pushnil(L_); }
@@ -587,7 +599,7 @@ private:
 public:
     template<class... SS>
     inline LuaDefStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
-        constexpr Counts counts = count_slots<0, 0, 0, 0>(stackslots...);
+        Counts counts = count_slots(stackslots...);
         int nargs = lua_gettop(L);
         if (counts.nextra == 0) {
             if (nargs != counts.narg) {
@@ -645,13 +657,10 @@ private:
 public:
     template<class... SS>
     LuaExtStack(lua_State *L, SS & ... stackslots) : LuaCoreStack(L) {
-        constexpr Counts counts = count_slots<0, 0, 0, 0>(stackslots...);
-        static_assert(counts.narg == 0, "LuaExtStack doesn't allow LuaArg parameters");
-        static_assert(counts.nret == 0, "LuaExtStack doesn't allow LuaRet parameters");
-        static_assert(counts.nextra == 0, "LuaExtStack doesn't allow LuaExtraArgs parameters");
-        lua_checkstack(L_, counts.nvar + 20);
+        int nvars = count_vars(stackslots...);
+        lua_checkstack(L_, nvars + 20);
         oldtop_ = lua_gettop(L_);
-        for (int i = 0; i < counts.nvar; i++) {
+        for (int i = 0; i < nvars; i++) {
             lua_pushnil(L_);
         }
         assign_slots(oldtop_ + 1, stackslots...);