diff --git a/src/ClaudeDo.Installer/Pages/WelcomePage/WelcomePageViewModel.cs b/src/ClaudeDo.Installer/Pages/WelcomePage/WelcomePageViewModel.cs
index 456be22..0f2c791 100644
--- a/src/ClaudeDo.Installer/Pages/WelcomePage/WelcomePageViewModel.cs
+++ b/src/ClaudeDo.Installer/Pages/WelcomePage/WelcomePageViewModel.cs
@@ -45,10 +45,15 @@ public partial class WelcomePageViewModel : ObservableObject, IInstallerPage
                 break;
 
             case InstallerMode.Update:
-                Heading = $"Update ClaudeDo  {_context.InstalledVersion}  ->  {_context.LatestVersion}";
+                Heading = $"Update ClaudeDo  {_context.InstalledVersion ?? "?"}  ->  {_context.LatestVersion ?? "?"}";
                 Subheading = "Your tasks, config, and database will be preserved. Click Next to continue.";
-                InstallDirEditable = false;
+                InstallDirEditable = false; // stay where we were installed
                 break;
+
+            default:
+                // Config and any future modes should never reach the wizard; guard loudly if they do.
+                throw new InvalidOperationException(
+                    $"WelcomePage is not valid for installer mode {_context.Mode}");
         }
 
         return Task.CompletedTask;