diff --git a/extension/script/backend/bootstrap.lua b/extension/script/backend/bootstrap.lua
index 6fa66113..45ab5b87 100644
--- a/extension/script/backend/bootstrap.lua
+++ b/extension/script/backend/bootstrap.lua
@@ -33,6 +33,7 @@ local function initMaster(rootpath, address)
     ExitGuard = setmetatable({}, {__gc=function()
         chan:push(nil, "EXIT")
         thread.wait(mt)
+        channel.destroy("DbgMaster")
     end})
 end
 
diff --git a/extension/script/backend/worker.lua b/extension/script/backend/worker.lua
index ac149ba5..82129993 100644
--- a/extension/script/backend/worker.lua
+++ b/extension/script/backend/worker.lua
@@ -829,6 +829,7 @@ end
 
 function event.exit()
     sendToMaster 'exitWorker' {}
+    channel.destroy(WorkerChannel)
 end
 
 hookmgr.init(function(name, ...)
diff --git a/extension/script/debugger.lua b/extension/script/debugger.lua
index 677241c7..cf9314e9 100644
--- a/extension/script/debugger.lua
+++ b/extension/script/debugger.lua
@@ -187,7 +187,7 @@ function dbg:start(cfg)
 end
 
 function dbg:attach(cfg)
-    initDebugger(self, cfg)
+    initDebugger(self, cfg or {})
 
     self.rdebug.start(([[
         local rootpath = %q
@@ -199,6 +199,10 @@ function dbg:attach(cfg)
     return self
 end
 
+function dbg:stop()
+    self.rdebug.clear()
+end
+
 function dbg:event(...)
     self.rdebug.event(...)
     return self
diff --git a/src/luadebug/rdebug_hookmgr.cpp b/src/luadebug/rdebug_hookmgr.cpp
index 4c246bdf..7315662a 100644
--- a/src/luadebug/rdebug_hookmgr.cpp
+++ b/src/luadebug/rdebug_hookmgr.cpp
@@ -568,6 +568,10 @@ struct hookmgr {
         }
         luadebug::eventfree::destroy(hL, eventfree);
         lua_sethook(hL, 0, 0, 0);
+#if defined(LUADEBUG_DISABLE_THUNK)
+        // clear hook manager pointer stored in thunk:
+        thunk_set(hL, &THUNK_MGR, intptr_t(nullptr));
+#endif
 #if defined(LUA_HOOKEXCEPTION)
         exception_open(hL, 0);
 #endif
@@ -594,11 +598,13 @@ struct hookmgr {
 #else
     static int full_hook_callback(lua_State* hL, lua_Debug* ar) {
         hookmgr* mgr = (hookmgr*)thunk_get(hL, &THUNK_MGR);
+        if (!mgr) return 0;
         mgr->full_hook(hL, ar);
         return 0;
     }
     static int idle_hook_callback(lua_State* hL, lua_Debug* ar) {
         hookmgr* mgr = (hookmgr*)thunk_get(hL, &THUNK_MGR);
+        if (!mgr) return 0;
         mgr->idle_hook(hL, ar);
         return 0;
     }