diff --git a/src/App/Callback/CallbackSystemHandler.hpp b/src/App/Callback/CallbackSystemHandler.hpp
index cf18288b..1c2c846d 100644
--- a/src/App/Callback/CallbackSystemHandler.hpp
+++ b/src/App/Callback/CallbackSystemHandler.hpp
@@ -43,6 +43,8 @@ struct CallbackSystemHandler : Red::IScriptable
 
     void operator()(const Red::Handle<CallbackSystemEvent>& aEvent)
     {
+        std::unique_lock sync(callbackLock);
+
         if (!registered || !valid)
             return;
 
@@ -213,8 +215,10 @@ struct CallbackSystemHandler : Red::IScriptable
     CallbackLifetime lifetime{CallbackLifetime::Session};
     Core::Vector<Red::Handle<CallbackSystemTarget>> targets;
     bool targeted{false};
-    bool valid{true};
+
+    Red::SharedSpinLock callbackLock;
     bool registered{true};
+    bool valid{true};
 
     RTTI_IMPL_TYPEINFO(App::CallbackSystemHandler);
     RTTI_IMPL_ALLOCATOR();
diff --git a/xmake.lua b/xmake.lua
index 11b0cd19..bc155bcb 100644
--- a/xmake.lua
+++ b/xmake.lua
@@ -1,7 +1,7 @@
 set_xmakever("2.5.9")
 
 set_project("Codeware")
-set_version("1.12.2", {build = "%y%m%d%H%M"})
+set_version("1.12.3", {build = "%y%m%d%H%M"})
 
 set_arch("x64")
 set_languages("cxx2a")