diff --git a/src/actsim_agent/worker.cpp b/src/actsim_agent/worker.cpp
index 98eb934..012ae03 100644
--- a/src/actsim_agent/worker.cpp
+++ b/src/actsim_agent/worker.cpp
@@ -39,7 +39,8 @@ void Worker::cancel_current() {
 }
 
 void Worker::join() {
-    worker_thread->join();
+    if (this->worker_thread != nullptr) return;
+    this->worker_thread->join();
 }
 
 void Worker::thread_run() {