diff --git a/CRSim/App.xaml.cs b/CRSim/App.xaml.cs
index 4123f7d..a7a68ee 100644
--- a/CRSim/App.xaml.cs
+++ b/CRSim/App.xaml.cs
@@ -6,10 +6,18 @@
         public static MainWindow MainWindow;
         public string[] commandLineArgs;
         public CommandLineOptions parsedOptions;
-        public static string AppVersion { get; set; } = Assembly.GetAssembly(typeof(App)).GetName().Version.ToString(); 
+        public static string AppVersion { get; set; } = Assembly.GetAssembly(typeof(App)).GetName().Version.ToString();
+        private Mutex mutex;
 
         public App()
         {
+            bool isNewInstance;
+            mutex = new Mutex(true,"CRSim",out isNewInstance);
+            if (!isNewInstance)
+            {
+                Environment.Exit(0);
+            }
+
             var args = Environment.GetCommandLineArgs();
             parsedOptions = CommandLineParser.Parse(args);
             if (parsedOptions.Debug)
diff --git a/CRSim/Properties/GlobalUsing.cs b/CRSim/Properties/GlobalUsing.cs
index 71cc718..c5a27e9 100644
--- a/CRSim/Properties/GlobalUsing.cs
+++ b/CRSim/Properties/GlobalUsing.cs
@@ -8,6 +8,7 @@ global using System.Collections.Generic;
 global using System.Collections.ObjectModel;
 global using System.Reflection;
 global using System.Timers;
+global using System.Threading;
 
 global using Microsoft.UI.Xaml;
 global using Microsoft.UI.Xaml.Controls;