diff --git a/src/win32cpp/ApplicationThread.cpp b/src/win32cpp/ApplicationThread.cpp
index 9a105114a..46340a8e1 100644
--- a/src/win32cpp/ApplicationThread.cpp
+++ b/src/win32cpp/ApplicationThread.cpp
@@ -86,7 +86,10 @@ bool ApplicationThread::InMainThread()
 //////////////////////////////////////////
 void ApplicationThread::AddCall(CallClassBase *callClass)
 {
-    this->calls.push_back(CallClassPtr(callClass));
+    {
+        boost::mutex::scoped_lock lock(this->mutex);
+        this->calls.push_back(CallClassPtr(callClass));
+    }
     this->NotifyMainThread();
 }