diff --git a/source/Cosmos.Build.Builder/App.xaml.cs b/source/Cosmos.Build.Builder/App.xaml.cs
index 00c4160ad..7f2e3eea8 100644
--- a/source/Cosmos.Build.Builder/App.xaml.cs
+++ b/source/Cosmos.Build.Builder/App.xaml.cs
@@ -20,6 +20,7 @@ namespace Cosmos.Build.Builder
             if (Process.GetProcessesByName("Cosmos.Build.Builder").Skip(1).Any())
             {
                 ShowErrorMessageBox("Cannot run more than 1 instance of builder at the same time!");
+                Current.Shutdown();
                 return;
             }