diff --git a/readme.md b/readme.md
index f50fc66..edb7f66 100644
--- a/readme.md
+++ b/readme.md
@@ -178,7 +178,7 @@ kubectl apply -f https://raw.githubusercontent.com/dockur/windows/refs/heads/mas
 
   By default, a user called `Docker` (with an empty password) is created during installation.
 
-  If you want to use different credentials, you can configure them (only BEFORE installation) in your compose file:
+  If you want to use different credentials, you can configure them in your compose file (only before installation):
 
   ```yaml
   environment:
@@ -201,13 +201,23 @@ kubectl apply -f https://raw.githubusercontent.com/dockur/windows/refs/heads/mas
 
 ### How do I select the keyboard layout?
 
-  If you want to use a keyboard layout or locale that is not the default for your selected language, before installation you can add  `KEYBOARD` and `REGION` variables like this:
+  If you want to use a keyboard layout or locale that is not the default for your selected language, you can add  `KEYBOARD` and `REGION` variables like this (before installation):
 
   ```yaml
   environment:
     REGION: "en-US"
     KEYBOARD: "en-US"
   ```
+
+### How do I set the product key?
+
+  By default, an evaluation version of Windows will be installed, but if you have product key you can add a `KEY` variable like this (before installation):
+
+  ```yaml
+  environment:
+    KEY: "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX"
+  ```
+
 ### How do I install a custom image?
 
   In order to download an unsupported ISO image, specify its URL in the `VERSION` environment variable:
diff --git a/src/define.sh b/src/define.sh
index 89ce2cc..04cdf82 100644
--- a/src/define.sh
+++ b/src/define.sh
@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
+: "${KEY:=""}"
 : "${WIDTH:=""}"
 : "${HEIGHT:=""}"
 : "${VERIFY:=""}"
@@ -1175,9 +1176,7 @@ prepareInstall() {
 
   local dir="$2"
   local desc="$3"
-  local arch="$4"
-  local key="$5"
-  local driver="$6"
+  local driver="$4"
   local drivers="/tmp/drivers"
 
   rm -rf "$drivers"
@@ -1196,7 +1195,8 @@ prepareInstall() {
     error "Failed to extract drivers!" && return 1
   fi
 
-  local target
+  local arch target
+  [ -d "$dir/AMD64" ] && arch="amd64" || arch="x86"
   [[ "${arch,,}" == "x86" ]] && target="$dir/I386" || target="$dir/AMD64"
 
   if [ ! -f "$drivers/viostor/$driver/$arch/viostor.sys" ]; then
@@ -1282,6 +1282,24 @@ prepareInstall() {
   [ -n "$PASSWORD" ] && password="$PASSWORD"
   [ -n "$USERNAME" ] && username=$(echo "$USERNAME" | sed 's/[^[:alnum:]@!._-]//g')
 
+  if [[ "${driver,,}" == "xp" ]]; then
+    if [[ "${arch,,}" == "x86" ]]; then
+      # Windows XP Professional x86 generic key (no activation, trial-only)
+      [ -z "$KEY" ] && KEY="DR8GV-C8V6J-BYXHG-7PYJR-DB66Y"
+    else
+      # Windows XP Professional x64 generic key (no activation, trial-only)
+      [ -z "$KEY" ] && KEY="B2RBK-7KPT9-4JP6X-QQFWM-PJD6G"
+    fi
+  else
+    if [[ "${arch,,}" == "x86" ]]; then
+      # Windows Server 2003 Standard x86 generic key (no activation, trial-only)
+      [ -z "$KEY" ] && KEY="QKDCQ-TP2JM-G4MDG-VR6F2-P9C48"
+    else
+      # Windows Server 2003 Standard x64 generic key (no activation, trial-only)
+      [ -z "$KEY" ] && KEY="P4WJG-WK3W7-3HM8W-RWHCK-8JTRY"
+    fi
+  fi
+
   find "$target" -maxdepth 1 -type f -iname winnt.sif -exec rm {} \;
 
   {       echo "[Data]"
@@ -1319,7 +1337,7 @@ prepareInstall() {
           echo "    FullName=\"$username\""
           echo "    ComputerName=\"*\""
           echo "    OrgName=\"Windows for Docker\""
-          echo "    ProductKey=$key"
+          echo "    ProductKey=$KEY"
           echo ""
           echo "[Identification]"
           echo "    JoinWorkgroup = WORKGROUP"
@@ -1465,56 +1483,6 @@ prepareInstall() {
   return 0
 }
 
-prepare2k3() {
-
-  local iso="$1"
-  local dir="$2"
-  local desc="$3"
-  local driver="2k3"
-  local arch key
-
-  [ -d "$dir/AMD64" ] && arch="amd64" || arch="x86"
-
-  if [[ "${arch,,}" == "x86" ]]; then
-    # Windows Server 2003 Standard x86 generic key (no activation, trial-only)
-    # This is not a pirated key, it comes from the official MS documentation.
-    key="QKDCQ-TP2JM-G4MDG-VR6F2-P9C48"
-  else
-    # Windows Server 2003 Standard x64 generic key (no activation, trial-only)
-    # This is not a pirated key, it comes from the official MS documentation.
-    key="P4WJG-WK3W7-3HM8W-RWHCK-8JTRY"
-  fi
-
-  prepareInstall "$iso" "$dir" "$desc" "$arch" "$key" "$driver" || return 1
-
-  return 0
-}
-
-prepareXP() {
-
-  local iso="$1"
-  local dir="$2"
-  local desc="$3"
-  local driver="xp"
-  local arch key
-
-  [ -d "$dir/AMD64" ] && arch="amd64" || arch="x86"
-
-  if [[ "${arch,,}" == "x86" ]]; then
-    # Windows XP Professional x86 generic key (no activation, trial-only)
-    # This is not a pirated key, it comes from the official MS documentation.
-    key="DR8GV-C8V6J-BYXHG-7PYJR-DB66Y"
-  else
-    # Windows XP Professional x64 generic key (no activation, trial-only)
-    # This is not a pirated key, it comes from the official MS documentation.
-    key="B2RBK-7KPT9-4JP6X-QQFWM-PJD6G"
-  fi
-
-  prepareInstall "$iso" "$dir" "$desc" "$arch" "$key" "$driver" || return 1
-
-  return 0
-}
-
 prepareLegacy() {
 
   local iso="$1"
@@ -1601,11 +1569,11 @@ setMachine() {
     "win2k"* )
       ETFS="[BOOT]/Boot-NoEmul.img" ;;
     "winxp"* )
-      if ! prepareXP "$iso" "$dir" "$desc"; then
+      if ! prepareInstall "$iso" "$dir" "$desc" "xp"; then
         error "Failed to prepare $desc ISO!" && return 1
       fi ;;
     "win2003"* )
-      if ! prepare2k3 "$iso" "$dir" "$desc"; then
+      if ! prepareInstall "$iso" "$dir" "$desc" "2k3"; then
         error "Failed to prepare $desc ISO!" && return 1
       fi ;;
   esac
diff --git a/src/install.sh b/src/install.sh
index 2a322be..003b302 100644
--- a/src/install.sh
+++ b/src/install.sh
@@ -681,6 +681,11 @@ updateXML() {
     sed -i "s/SERVERSTANDARD<\/Value>/SERVER${EDITION^^}<\/Value>/g" "$asset"
   fi
 
+  if [ -n "$KEY" ]; then
+    sed -i '/<ProductKey>/,/<\/ProductKey>/d' "$asset"
+    sed -i "s/<\/UserData>/  <ProductKey>\n          <Key>${KEY}<\/Key>\n          <WillShowUI>OnError<\/WillShowUI>\n        <\/ProductKey>\n      <\/UserData>/g" "$asset"
+  fi
+
   return 0
 }