diff --git a/src/ssl.c b/src/ssl.c
index d7b7243..1e4c6c4 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -848,5 +848,9 @@ LSEC_API int luaopen_ssl_core(lua_State *L)
 
   luaL_newlib(L, funcs);
 
+  lua_pushstring(L, "SOCKET_INVALID");
+  lua_pushnumber(L, SOCKET_INVALID);
+  lua_rawset(L, -3);
+
   return 1;
 }
diff --git a/src/ssl.lua b/src/ssl.lua
index 8ea2b2b..edc0862 100644
--- a/src/ssl.lua
+++ b/src/ssl.lua
@@ -120,7 +120,7 @@ local function wrap(sock, cfg)
    local s, msg = core.create(ctx)
    if s then
       core.setfd(s, sock:getfd())
-      sock:setfd(-1)
+      sock:setfd(core.SOCKET_INVALID)
       registry[s] = ctx
       return s
    end