diff --git a/wix/main.wxs b/wix/main.wxs
index 2efdd50..2735064 100644
--- a/wix/main.wxs
+++ b/wix/main.wxs
@@ -8,9 +8,14 @@
 
 <Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
     <Product Id="*" UpgradeCode="C19F9B41-CD13-4F0E-B27D-E0EF8CF1CE91" Version="0.1.0" Language="1033" Name="Grim" Manufacturer="Ardocrat">
-        <Package InstallerVersion="300" Compressed="yes"/>
+        <Package Id="7a18ee67-b049-4462-b18f-9e7748685781" InstallerVersion="300" Compressed="yes"/>
         <Media Id="1" Cabinet="grim.cab" EmbedCab="yes" />
 
+        <MajorUpgrade
+            DowngradeErrorMessage = "A newer version of [ProductName] is already installed."
+            AllowSameVersionUpgrades = "yes"
+        />
+
         <Icon Id='ProductICO' SourceFile='wix\Product.ico'/>
         <Property Id='ARPPRODUCTICON' Value='ProductICO' />