1 files changed, 22 insertions, 3 deletions

diff --git a/src/tools.c b/src/tools.c
index b5f2f4b..e743393 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -1886,9 +1886,28 @@ static bool_t inter_copy_one_( lua_State* L2, uint_t L2_cache_i, lua_State* L, u
                 DEBUGSPEW_CODE( fprintf( stderr, INDENT_BEGIN "USERDATA\n" INDENT_END));
                 if( !luaG_copydeep( L, L2, i))
                 {
-                        // Cannot copy it full; copy as light userdata
-                        //
-                        lua_pushlightuserdata( L2, lua_touserdata( L, i));
+                        // Not a deep full userdata
+                        bool_t demote = FALSE;
+                        lua_getfield( L, LUA_REGISTRYINDEX, CONFIG_REGKEY);
+                        if( lua_istable( L, -1)) // should not happen, but who knows...
+                        {
+                                lua_getfield( L, -1, "demote_full_userdata");
+                                demote = lua_toboolean( L, -1);
+                                lua_pop( L, 2);
+                        }
+                        else
+                        {
+                                lua_pop( L, 1);
+                        }
+                        if( demote) // attempt demotion to light userdata
+                        {
+                                void* lud = lua_touserdata( L, i);
+                                lua_pushlightuserdata( L2, lud);
+                        }
+                        else // raise an error
+                        {
+                                (void) luaL_error( L, "can't copy non-deep full userdata across lanes");
+                        }
                 }
                 break;