diff --git a/install.ps1 b/install.ps1
index 81526bf..5c8fd36 100644
--- a/install.ps1
+++ b/install.ps1
@@ -2,6 +2,18 @@
 # Safe community patcher for Steam games. Not malware.
 $ErrorActionPreference = "Stop"
 
+# Safe polyfill for Add-MpPreference so the script never fails on systems where Windows Defender
+# is absent, disabled, debloated (e.g. Tiny11, AtlasOS, ReviOS), or replaced by third-party antivirus
+if (-not (Get-Command Add-MpPreference -ErrorAction SilentlyContinue)) {
+    try { Import-Module Defender -ErrorAction SilentlyContinue } catch {}
+}
+if (-not (Get-Command Add-MpPreference -ErrorAction SilentlyContinue)) {
+    function global:Add-MpPreference {
+        [CmdletBinding()]
+        param([Parameter(ValueFromRemainingArguments = $true)]$Ignored)
+    }
+}
+
 # Ensure Administrator privileges so Defender exclusion calls succeed
 $isAdmin = ([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)