How can I execute a Lua callback from C (asynchronously)?

I want to call a function in Lua from a C library, but done asynchronously.

I have some Lua code that looks like this:

l = require "mylib"

l.subscribe(function ()
  print("Called")
  error("This is an error")
end)

mylib is implemented using the Lua C API. It looks a bit like this.

struct cb {
  int ref;
  lua_State *state;
}

int number_callbacks;
struct **cb callback_functions;

static int subscribe(lua_State *L) {

  lua_settop(L, 1);
  luaL_checktype(L, 1, LUA_TFUNCTION);

  struct cb c;
  c.ref = luaL_ref(L, LUA_REGISTRYINDEX);
  c.state = L;

  // store c in callback_functions
}

// foo is registered as a callback to another C lib and
// is called occasionaly
static void foo(int callback_code) {

   for (int i = 0; i < number_callbacks; i++) {

     struct cb c = callback_functions[i];
     lua_rawgeti(c->state, LUA_REGISTRYINDEX, c->ref);
     lua_pushinteger(c->state, callback_code);

     int ret = lua_pcall(c->state, 1, 0, 0);

     // Check ret...
   }
}

The message in the callback is printed, however the error shows up in the wrong place (it says it was caused by some unrelated function). I assume this is because the Lua state has changed.

What is the proper way to do this?