diff --git a/installer/main.wxs b/installer/main.wxs
index b5ca3ba3..df33ce31 100644
--- a/installer/main.wxs
+++ b/installer/main.wxs
@@ -81,6 +81,13 @@
         <Property Id="ARPNOREPAIR" Value="1" />
         <Property Id="ARPSIZE" Value="10000" />
 
+        <!-- Without this, Windows Installer uses the Restart Manager in silent mode to shut down every
+            process that holds one of the package's files, before ServiceControl stops the service. It ran
+            during every upgrade, repair and uninstall, where GitHub-hosted runners intermittently lost
+            their runner agent. ServiceControl and KillProcess already stop the exporter of this
+            installation. -->
+        <Property Id="MSIRESTARTMANAGERCONTROL" Value="Disable" />
+
         <Property Id="START_MENU_FOLDER" Value="0" />
         <Property Id="NOSTART" Value="0" />
 
diff --git a/tools/test-installer.ps1 b/tools/test-installer.ps1
index 4a249aad..1b4dc60b 100644
--- a/tools/test-installer.ps1
+++ b/tools/test-installer.ps1
@@ -76,7 +76,7 @@ function Write-MsiexecDiagnostic([String] $Log, [DateTime] $Since) {
     }
 }
 
-function Invoke-Msiexec([String] $Name, [String[]] $Arguments) {
+function Invoke-Msiexec([String] $Name, [String[]] $Arguments, [Switch] $PreviousPackage) {
     $log = Join-Path $WorkDir "$Name.log"
     $allArguments = $Arguments + @('/qn', '/norestart', '/L*v', "`"$log`"")
     Write-Host "msiexec $($allArguments -join ' ')"
@@ -87,6 +87,17 @@ function Invoke-Msiexec([String] $Name, [String[]] $Arguments) {
     Write-Host "  msiexec $Name took $([Math]::Round(((Get-Date) - $since).TotalSeconds, 1)) s, exit code $($process.ExitCode)"
     Write-Host "  runner after: $(Get-RunnerProcess)"
     Write-MsiexecDiagnostic -Log $log -Since $since
+
+    # The package disables the Restart Manager, so no operation may shut down
+    # applications that hold its files. An upgrade removes the previous release
+    # with the previous package's settings, which still enable it.
+    if (-not $PreviousPackage -and (Test-Path $log)) {
+        $shutdown = Select-String -Path $log -Encoding unicode -Pattern 'RESTART MANAGER: Successfully shut down'
+        if ($null -ne $shutdown) {
+            throw "msiexec $Name let the Restart Manager shut down applications, see $log"
+        }
+    }
+
     # 3010 means success, but a restart is required.
     if ($process.ExitCode -ne 0 -and $process.ExitCode -ne 3010) {
         throw "msiexec $Name failed with exit code $($process.ExitCode), see $log"
@@ -204,7 +215,7 @@ try {
         throw "checksum mismatch for $previousMsi`: $actualHash, expected $expectedHash"
     }
 
-    Invoke-Msiexec -Name 'install-previous' -Arguments @('/i', "`"$previousMsi`"")
+    Invoke-Msiexec -Name 'install-previous' -Arguments @('/i', "`"$previousMsi`"") -PreviousPackage
     Assert-ServiceRunning | Out-Null
     Write-Host '::endgroup::'
 
@@ -217,7 +228,7 @@ try {
 
     Write-Step 'Upgrade to this build'
     Start-Foreign
-    Invoke-Msiexec -Name 'upgrade' -Arguments @('/i', "`"$UpgradeMsi`"")
+    Invoke-Msiexec -Name 'upgrade' -Arguments @('/i', "`"$UpgradeMsi`"") -PreviousPackage
     $metrics = Assert-ServiceRunning
     Assert-InstalledExecutable