diff --git a/tools/simulators.cpp b/tools/simulators.cpp
index a88bb64..c4085ac 100644
--- a/tools/simulators.cpp
+++ b/tools/simulators.cpp
@@ -75,6 +75,7 @@ std::vector<std::string> Simulators::list_simulators() const
 
 Simulator_base* Simulators::invoke_active_simulator()
 {
+    std::lock_guard<std::mutex> lock(m_mutex);
     if (this->m_simulators.empty())
     {
         return nullptr;
@@ -91,6 +92,7 @@ Simulator_base* Simulators::invoke_active_simulator()
 
 json Simulators::changed_UI_items()
 {
+    std::lock_guard<std::mutex> lock(m_mutex);
     if (this->m_simulators.empty())
     {
         return "{}"_json;
diff --git a/tools/simulators.hpp b/tools/simulators.hpp
index 3b373af..cd483db 100644
--- a/tools/simulators.hpp
+++ b/tools/simulators.hpp
@@ -1,6 +1,7 @@
 #pragma once
 #include <memory>
 #include <map>
+#include <mutex>
 
 #include "simulator_base.hpp"
 
@@ -19,5 +20,6 @@ class Simulators {
     private:
         std::map<std::string, std::unique_ptr<Simulator_base>> m_simulators;
         std::string m_current_simulator = "";
+        std::mutex m_mutex;
         json m_before;
 };
\ No newline at end of file