diff --git a/.github/workflows/installer-smoke.yml b/.github/workflows/installer-smoke.yml
index a8c048d9f..a4c971c81 100644
--- a/.github/workflows/installer-smoke.yml
+++ b/.github/workflows/installer-smoke.yml
@@ -23,13 +23,17 @@ jobs:
       - name: Run installer dry-run
         run: bash scripts/install.sh --dry-run --verbose
 
-  # smoke-windows:
-  #   name: Smoke install.ps1 (windows-latest)
-  #   runs-on: windows-latest
-  #   steps:
-  #     - name: Checkout
-  #       uses: actions/checkout@v4
+  smoke-windows:
+    name: install.ps1 tests + dry-run (windows-latest)
+    runs-on: windows-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
 
-  #     - name: Run installer dry-run
-  #       shell: pwsh
-  #       run: ./scripts/install.ps1 -DryRun
+      - name: Unit tests (MSI args / asset selection)
+        shell: pwsh
+        run: pwsh -NoProfile -File ./scripts/tests/OpenHumanWindowsInstall.Tests.ps1
+
+      - name: Run installer dry-run
+        shell: pwsh
+        run: ./scripts/install.ps1 -DryRun
diff --git a/package.json b/package.json
index 042d78b91..148af9e1e 100644
--- a/package.json
+++ b/package.json
@@ -27,6 +27,7 @@
     "review": "bash scripts/review/cli.sh",
     "work": "bash scripts/work/cli.sh",
     "debug": "bash scripts/debug/cli.sh",
+    "test:install-ps1": "pwsh -NoProfile -File scripts/tests/OpenHumanWindowsInstall.Tests.ps1",
     "rust:check": "pnpm --filter openhuman-app rust:check",
     "typecheck": "pnpm --filter openhuman-app compile"
   },
diff --git a/scripts/install.ps1 b/scripts/install.ps1
index 8e38dc268..c6dedb4f5 100644
--- a/scripts/install.ps1
+++ b/scripts/install.ps1
@@ -9,8 +9,72 @@
 
   Also works when saved and run directly:
   .\scripts\install.ps1 -DryRun
+
+  MSI installs use the Tauri WiX package (InstallScope perMachine). Per-user
+  public properties (MSIINSTALLPERUSER / ALLUSERS=2) conflict with that layout
+  and commonly fail with exit 1603 — see tinyhumansai/openhuman#913.
+
+  When the current session is not elevated, msiexec is started with -Verb RunAs
+  so Windows shows UAC once (machine install to Program Files).
 #>
 
+# --- Script-scoped helpers (unit-tested; safe to dot-source this file) ---
+
+function Get-OpenHumanMsiexecInstallArgumentList {
+  <#
+  .SYNOPSIS
+    Argument list for Start-Process msiexec.exe (no per-user MSI overrides).
+  #>
+  param(
+    [Parameter(Mandatory = $true)]
+    [string]$MsiPath
+  )
+  # Pass -ArgumentList as string[]: each entry is one argv token for msiexec, so spaces in
+  # $MsiPath do not split. Do not wrap $MsiPath in extra literal " characters here — that can
+  # double-escape when Start-Process builds the native command line (see PR #1187 review).
+  return @('/i', $MsiPath, '/qn', '/norestart')
+}
+
+function Test-OpenHumanWindowsProcessElevated {
+  <#
+  .SYNOPSIS
+    True when the current process is running with an administrator token (Windows only).
+  #>
+  if ($env:OS -ne 'Windows_NT') {
+    return $false
+  }
+  $identity = [Security.Principal.WindowsIdentity]::GetCurrent()
+  $principal = [Security.Principal.WindowsPrincipal]::new($identity)
+  return $principal.IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)
+}
+
+function Select-OpenHumanWindowsAssetFromRelease {
+  <#
+  .SYNOPSIS
+    Pick the Windows x64 MSI from a GitHub release object, else NSIS exe.
+  #>
+  param(
+    [Parameter(Mandatory = $true)]
+    [object]$Release
+  )
+  $assets = @($Release.assets)
+  if (-not $assets -or $assets.Count -eq 0) {
+    return $null
+  }
+
+  $msi = $assets | Where-Object { $_.name -match 'OpenHuman_.*x64.*\.msi$' } | Select-Object -First 1
+  if ($msi) {
+    return $msi
+  }
+
+  $exe = $assets | Where-Object { $_.name -match 'OpenHuman_.*x64.*\.exe$' } | Select-Object -First 1
+  if ($exe) {
+    return $exe
+  }
+
+  return $null
+}
+
 # Wrap in a function so `param()` works when piped via `irm | iex`.
 # When piped, PowerShell cannot bind param() at the top-level scope.
 function Install-OpenHuman {
@@ -23,7 +87,7 @@ function Install-OpenHuman {
 
   $ErrorActionPreference = "Stop"
 
-  $InstallerVersion = "1.0.0"
+  $InstallerVersion = "1.1.0"
   $Repo = "tinyhumansai/openhuman"
   $LatestReleaseApiUrl = "https://api.github.com/repos/$Repo/releases/latest"
 
@@ -90,25 +154,10 @@ Examples:
   $assetUrl = ""
   $assetDigest = ""
 
-  function Select-WindowsAssetFromRelease([object]$Rel) {
-    $assets = @($Rel.assets)
-    if (-not $assets -or $assets.Count -eq 0) {
-      return $null
-    }
-
-    $msi = $assets | Where-Object { $_.name -match 'OpenHuman_.*x64.*\.msi$' } | Select-Object -First 1
-    if ($msi) { return $msi }
-
-    $exe = $assets | Where-Object { $_.name -match 'OpenHuman_.*x64.*\.exe$' } | Select-Object -First 1
-    if ($exe) { return $exe }
-
-    return $null
-  }
-
   try {
     $release = Invoke-RestMethod -Uri $LatestReleaseApiUrl -UseBasicParsing
     $releaseTag = ($release.tag_name -replace '^v', '')
-    $selected = Select-WindowsAssetFromRelease -Rel $release
+    $selected = Select-OpenHumanWindowsAssetFromRelease -Release $release
     if ($selected) {
       $assetName = $selected.name
       $assetUrl = $selected.browser_download_url
@@ -155,7 +204,13 @@ Examples:
 
   if ($DryRun) {
     if ($assetName -like "*.msi") {
-      Write-Output "DRY RUN: msiexec /i `"$tmpFile`" MSIINSTALLPERUSER=1 ALLUSERS=2 /qn /norestart"
+      $dryMsiArgs = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $tmpFile
+      Write-Output "DRY RUN: msiexec ArgumentList = $($dryMsiArgs | ConvertTo-Json -Compress)"
+      if (Test-OpenHumanWindowsProcessElevated) {
+        Write-Output "DRY RUN: (already elevated) Start-Process msiexec -Wait -ArgumentList <above>"
+      } else {
+        Write-Output "DRY RUN: (non-admin) Start-Process msiexec -Verb RunAs -Wait -ArgumentList <above>"
+      }
     } else {
       Write-Output "DRY RUN: Start-Process `"$tmpFile`" -Wait"
     }
@@ -164,10 +219,17 @@ Examples:
 
   Write-Info "Installing OpenHuman"
   if ($assetName -like "*.msi") {
-    $msiArgs = "/i `"$tmpFile`" MSIINSTALLPERUSER=1 ALLUSERS=2 /qn /norestart"
-    $proc = Start-Process -FilePath "msiexec.exe" -ArgumentList $msiArgs -Wait -PassThru
+    $msiArgs = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $tmpFile
+    $elevated = Test-OpenHumanWindowsProcessElevated
+    if ($elevated) {
+      $proc = Start-Process -FilePath "msiexec.exe" -ArgumentList $msiArgs -Wait -PassThru
+    } else {
+      Write-Info "Requesting administrator approval for machine-wide install (UAC)…"
+      $proc = Start-Process -FilePath "msiexec.exe" -ArgumentList $msiArgs -Verb RunAs -Wait -PassThru
+    }
     if ($proc.ExitCode -ne 0) {
       Write-Err "MSI install failed with exit code $($proc.ExitCode)."
+      Write-WarnMsg "If this persists, capture a log: msiexec /i `"$tmpFile`" /l*v `"$env:TEMP\OpenHuman-msi.log`""
       return
     }
   } elseif ($assetName -like "*.exe") {
@@ -199,5 +261,7 @@ Examples:
   }
 }
 
-# Run the installer, forwarding any arguments passed when invoked as a file.
-Install-OpenHuman @args
+# Run when executed as a script; skip when dot-sourced (e.g. unit tests).
+if ($MyInvocation.InvocationName -ne '.') {
+  Install-OpenHuman @args
+}
diff --git a/scripts/tests/OpenHumanWindowsInstall.Tests.ps1 b/scripts/tests/OpenHumanWindowsInstall.Tests.ps1
new file mode 100644
index 000000000..965bbdcab
--- /dev/null
+++ b/scripts/tests/OpenHumanWindowsInstall.Tests.ps1
@@ -0,0 +1,99 @@
+#!/usr/bin/env pwsh
+<#
+.SYNOPSIS
+  Unit tests for scripts/install.ps1 helpers (#913 MSI argument contract).
+
+.DESCRIPTION
+  Dot-sources install.ps1 (does not run Install-OpenHuman) and validates
+  Get-OpenHumanMsiexecInstallArgumentList, Select-OpenHumanWindowsAssetFromRelease,
+  and Test-OpenHumanWindowsProcessElevated.
+
+  Run from repo root:
+    pwsh -NoProfile -File scripts/tests/OpenHumanWindowsInstall.Tests.ps1
+#>
+$ErrorActionPreference = 'Stop'
+
+$installScript = (Resolve-Path (Join-Path (Join-Path $PSScriptRoot '..') 'install.ps1')).Path
+. $installScript
+
+$testCount = 0
+$failCount = 0
+
+function Assert-Equal {
+  param(
+    [string]$Expected,
+    [string]$Actual,
+    [string]$Message
+  )
+  $script:testCount++
+  if ($Expected -ne $Actual) {
+    $script:failCount++
+    Write-Host "FAIL: $Message" -ForegroundColor Red
+    Write-Host "  expected: $Expected" -ForegroundColor Red
+    Write-Host "  actual:   $Actual" -ForegroundColor Red
+  } else {
+    Write-Host "ok $Message" -ForegroundColor Green
+  }
+}
+
+function Assert-True {
+  param([bool]$Condition, [string]$Message)
+  $script:testCount++
+  if (-not $Condition) {
+    $script:failCount++
+    Write-Host "FAIL: $Message" -ForegroundColor Red
+  } else {
+    Write-Host "ok $Message" -ForegroundColor Green
+  }
+}
+
+Write-Host "`n== Get-OpenHumanMsiexecInstallArgumentList (#913) ==" -ForegroundColor Cyan
+$p = 'C:\Temp\OpenHuman_0.0.0_x64_en-US.msi'
+$args = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $p
+Assert-True ($args.Count -eq 4) 'returns exactly 4 argument tokens'
+Assert-Equal '/i' $args[0] 'first token is /i'
+Assert-Equal $p $args[1] 'second token is MSI path'
+$pSpaces = 'C:\Temp\Test User\OpenHuman_0.0.0_x64_en-US.msi'
+$argsSpaces = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $pSpaces
+Assert-Equal $pSpaces $argsSpaces[1] 'path with spaces remains one second argv token (no split)'
+Assert-Equal '/qn' $args[2] 'third token is /qn'
+Assert-Equal '/norestart' $args[3] 'fourth token is /norestart'
+Assert-True ($args -notcontains 'MSIINSTALLPERUSER') 'must not set MSIINSTALLPERUSER (perMachine MSI)'
+Assert-True ($args -notcontains 'ALLUSERS=2') 'must not set ALLUSERS=2'
+Assert-True ($args -notcontains 'ALLUSERS=1') 'must not set ALLUSERS=1 (use package default)'
+$joined = $args -join ' '
+Assert-True ($joined -notmatch 'MSIINSTALLPERUSER') 'joined args omit MSIINSTALLPERUSER'
+Assert-True ($joined -notmatch 'ALLUSERS') 'joined args omit ALLUSERS'
+
+Write-Host "`n== Select-OpenHumanWindowsAssetFromRelease ==" -ForegroundColor Cyan
+$release = [pscustomobject]@{
+  assets = @(
+    [pscustomobject]@{ name = 'OpenHuman_1.0.0_x64_en-US.msi'; browser_download_url = 'https://example/msi' }
+    [pscustomobject]@{ name = 'other.zip'; browser_download_url = 'https://example/z' }
+  )
+}
+$sel = Select-OpenHumanWindowsAssetFromRelease -Release $release
+Assert-Equal 'OpenHuman_1.0.0_x64_en-US.msi' $sel.name 'prefers MSI over other assets'
+
+$releaseExe = [pscustomobject]@{
+  assets = @(
+    [pscustomobject]@{ name = 'OpenHuman_1.0.0_x64-setup.exe'; browser_download_url = 'https://example/exe' }
+  )
+}
+$sel2 = Select-OpenHumanWindowsAssetFromRelease -Release $releaseExe
+Assert-True ($null -ne $sel2) 'selects exe when no msi'
+Assert-Equal 'OpenHuman_1.0.0_x64-setup.exe' $sel2.name 'exe name matches pattern'
+
+$releaseEmpty = [pscustomobject]@{ assets = @() }
+$sel3 = Select-OpenHumanWindowsAssetFromRelease -Release $releaseEmpty
+Assert-True ($null -eq $sel3) 'null when no assets'
+
+Write-Host "`n== Test-OpenHumanWindowsProcessElevated ==" -ForegroundColor Cyan
+$t = Test-OpenHumanWindowsProcessElevated
+Assert-True ($t -is [bool]) 'returns a boolean'
+
+Write-Host "`n== $($testCount) checks, $failCount failed ==" -ForegroundColor $(if ($failCount -eq 0) { 'Green' } else { 'Red' })
+if ($failCount -gt 0) {
+  exit 1
+}
+exit 0