diff --git a/windows/installer/build.ps1 b/windows/installer/build.ps1
index 32499ce..eb151b6 100644
--- a/windows/installer/build.ps1
+++ b/windows/installer/build.ps1
@@ -144,9 +144,12 @@ function Invoke-Repack {
     $etfs = Join-Path $isoRoot 'boot\etfsboot.com'
     $efi  = Join-Path $isoRoot 'efi\microsoft\boot\efisys.bin'
     if (-not (Test-Path $efi)) { throw "missing UEFI boot image: $efi" }
-    $bootdata = '2#p0,e,b"{0}"#pEF,e,b"{1}"' -f $etfs, $efi
+    # Work paths have no spaces (SYSTEM TEMP / runner temp), so omit oscdimg's
+    # inner quotes around the boot images -- otherwise PowerShell mangles the
+    # native -bootdata arg into doubled quotes (oscdimg Error 123).
+    $bootdata = "2#p0,e,b$etfs#pEF,e,b$efi"
     if (Test-Path $OutputIso) { Remove-Item $OutputIso -Force }
-    & $oscdimg -m -o -u2 -udfver102 -l"SILVERMETAL" "-bootdata:$bootdata" $isoRoot $OutputIso
+    & $oscdimg -m -o -u2 -udfver102 -lSILVERMETAL "-bootdata:$bootdata" $isoRoot $OutputIso
     if ($LASTEXITCODE -ne 0) { throw "oscdimg failed ($LASTEXITCODE)" }
 }