diff --git a/release/Install-Windows.ps1 b/release/Install-Windows.ps1
index 047fcd86..5342036e 100644
--- a/release/Install-Windows.ps1
+++ b/release/Install-Windows.ps1
@@ -98,6 +98,7 @@ try {
         }
     }
     if ($platformCount -ne 1 -or $data.Count -eq 0 -or $assets.Count -ne ($data.Count + 1)) { throw 'Incomplete release asset manifest.' }
+    Add-Type -AssemblyName System.IO.Compression
     Add-Type -AssemblyName System.IO.Compression.FileSystem
     foreach ($asset in $assets) {
         $name = $asset.name
diff --git a/release/Test-Install-Windows.ps1 b/release/Test-Install-Windows.ps1
index c6f7b28f..66eeca14 100644
--- a/release/Test-Install-Windows.ps1
+++ b/release/Test-Install-Windows.ps1
@@ -2,6 +2,7 @@
 # network download, admin rights or long-path registry configuration is needed.
 param([string]$Installer = (Join-Path $PSScriptRoot 'Install-Windows.ps1'))
 $ErrorActionPreference = 'Stop'
+Add-Type -AssemblyName System.IO.Compression
 Add-Type -AssemblyName System.IO.Compression.FileSystem
 $temp = Join-Path ([IO.Path]::GetTempPath()) ('Raptor-installer-test-' + [guid]::NewGuid().ToString('N'))
 New-Item -ItemType Directory -Path $temp | Out-Null