diff --git a/src/ClaudeDo.Installer/Steps/RegisterServiceStep.cs b/src/ClaudeDo.Installer/Steps/RegisterServiceStep.cs
index ef29c15..40364e8 100644
--- a/src/ClaudeDo.Installer/Steps/RegisterServiceStep.cs
+++ b/src/ClaudeDo.Installer/Steps/RegisterServiceStep.cs
@@ -23,6 +23,24 @@ public sealed class RegisterServiceStep : IInstallStep
         progress.Report("Removing existing service registration (if any)...");
         await RunSc($"delete {ServiceName}", ctx, progress, ct, ignoreErrors: true);
 
+        // Wait for the service to actually disappear from SCM. `sc delete` returns
+        // immediately but the service stays "marked for deletion" until every open
+        // handle (services.msc, Task Manager, a prior sc query process) is closed.
+        // Poll up to 30s — then fail with actionable guidance if it's still there.
+        progress.Report("Waiting for prior service registration to clear...");
+        for (var i = 0; i < 30; i++)
+        {
+            ct.ThrowIfCancellationRequested();
+            var (queryExit, _) = await RunSc($"query {ServiceName}", ctx, progress, ct, ignoreErrors: true);
+            if (queryExit != 0) break; // service no longer registered — good
+            if (i == 29)
+                return StepResult.Fail(
+                    $"Service '{ServiceName}' is marked for deletion but hasn't cleared after 30s. " +
+                    "Close any open Services console (services.msc), Task Manager Services tab, or " +
+                    "Event Viewer showing the service, then retry. A reboot will also clear it.");
+            await Task.Delay(1000, ct);
+        }
+
         // Create service
         var startType = ctx.AutoStart ? "auto" : "demand";
         var createArgs = $"create {ServiceName} binPath= \"{workerExe}\" start= {startType}";
@@ -35,6 +53,10 @@ public sealed class RegisterServiceStep : IInstallStep
 
         progress.Report("Creating service...");
         var (exitCode, output) = await RunSc(createArgs, ctx, progress, ct);
+        if (exitCode == 1072)
+            return StepResult.Fail(
+                $"Service '{ServiceName}' is still marked for deletion. " +
+                "Close services.msc / Task Manager / Event Viewer and retry, or reboot.");
         if (exitCode != 0)
             return StepResult.Fail($"sc.exe create failed (exit {exitCode}): {output}");