diff --git a/src/Directory.csproj.props b/src/Directory.csproj.props
index 42407929a..6891ef2fc 100644
--- a/src/Directory.csproj.props
+++ b/src/Directory.csproj.props
@@ -2,7 +2,7 @@
 
 <Project>
   <PropertyGroup>
-    <LangVersion Condition=" '$(TargetFrameworkVersion)'=='' ">14.0</LangVersion>
+    <LangVersion Condition=" '$(TargetFrameworkVersion)'=='' ">13.0</LangVersion>
     <CheckForOverflowUnderflow>true</CheckForOverflowUnderflow>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>$([System.IO.Path]::GetFullPath($(MSBuildThisFileDirectory)wix.snk))</AssemblyOriginatorKeyFile>
diff --git a/src/burn/engine/relatedbundle.cpp b/src/burn/engine/relatedbundle.cpp
index 166c4ae83..2d95111fb 100644
--- a/src/burn/engine/relatedbundle.cpp
+++ b/src/burn/engine/relatedbundle.cpp
@@ -356,10 +356,19 @@ static HRESULT LoadRelatedBundleFromKey(
         LogId(REPORT_WARNING, MSG_RELATED_PACKAGE_INVALID_VERSION, wzRelatedBundleCode, sczBundleVersion);
     }
 
+    // Look for v7+ scope registration.
     hr = RegReadNumber(hkBundleCode, BURN_REGISTRATION_REGISTRY_BUNDLE_SCOPE, &dwScope);
-    ExitOnFailure(hr, "Failed to read registration %ls for bundle %ls.", wzRelatedBundleCode, BURN_REGISTRATION_REGISTRY_BUNDLE_SCOPE);
+    if (SUCCEEDED(hr))
+    {
+        pRelatedBundle->detectedScope = static_cast<BOOTSTRAPPER_SCOPE>(dwScope);
+    }
+    else if (E_FILENOTFOUND == hr)
+    {
+        hr = S_OK;
 
-    pRelatedBundle->detectedScope = static_cast<BOOTSTRAPPER_SCOPE>(dwScope);
+        pRelatedBundle->detectedScope = fPerMachine ? BOOTSTRAPPER_SCOPE_PER_MACHINE : BOOTSTRAPPER_SCOPE_PER_USER;
+    }
+    ExitOnFailure(hr, "Failed to read registration %ls for bundle %ls.", wzRelatedBundleCode, BURN_REGISTRATION_REGISTRY_BUNDLE_SCOPE);
 
     hr = RegReadString(hkBundleCode, BURN_REGISTRATION_REGISTRY_BUNDLE_CACHE_PATH, &sczCachePath);
     ExitOnFailure(hr, "Failed to read cache path from registry for bundle: %ls", wzRelatedBundleCode);
diff --git a/src/internal/SetBuildNumber/global.json.pp b/src/internal/SetBuildNumber/global.json.pp
index b99149d23..b1acc7130 100644
--- a/src/internal/SetBuildNumber/global.json.pp
+++ b/src/internal/SetBuildNumber/global.json.pp
@@ -6,7 +6,7 @@
     "WixToolset.Sdk": "{packageversion}"
   },
   "sdk": {
-    "version": "10.0.100",
+    "version": "9.0.300",
     "rollForward": "latestFeature"
   }
 }
diff --git a/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/Bundle.wxs b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/Bundle.wxs
index e170667b7..eb2a74ac3 100644
--- a/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/Bundle.wxs
+++ b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/Bundle.wxs
@@ -1,9 +1,11 @@
 <Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:bal="http://wixtoolset.org/schemas/v4/wxs/bal">
-  <Bundle Id="PerMachineBundle" Name="PerMachineBundle" Manufacturer="Acme" Version="1.0.0.0">
+  <Bundle Id="PerMachineBundle" Name="PerMachineBundle" Manufacturer="Acme" Version="$(Version)">
     <BootstrapperApplication>
       <bal:WixStandardBootstrapperApplication LicenseUrl="https://www.example.com/license" Theme="hyperlinkLicense" />
     </BootstrapperApplication>
 
+    <Variable Name="TestBundleId" Value="PerMachineBundle v$(Version)" />
+
     <Chain>
       <MsiPackage SourceFile="PerMachinePkg.msi" />
     </Chain>
diff --git a/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundle.wixproj b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundle.wixproj
index ade65220d..ed15dedf4 100644
--- a/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundle.wixproj
+++ b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundle.wixproj
@@ -1,6 +1,7 @@
 <Project Sdk="WixToolset.Sdk">
   <PropertyGroup>
     <OutputType>Bundle</OutputType>
+    <DefineConstants>$(DefineConstants);Version=1.0.0.0</DefineConstants>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="WixToolset.BootstrapperApplications.wixext" />
diff --git a/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundleV2.wixproj b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundleV2.wixproj
new file mode 100644
index 000000000..fcdbae054
--- /dev/null
+++ b/src/test/burn/TestData/ConfigurableScopeTests/PerMachineBundle/PerMachineBundleV2.wixproj
@@ -0,0 +1,12 @@
+<Project Sdk="WixToolset.Sdk">
+  <PropertyGroup>
+    <OutputType>Bundle</OutputType>
+    <DefineConstants>$(DefineConstants);Version=2.0.0.0</DefineConstants>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="WixToolset.BootstrapperApplications.wixext" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\PerMachinePkg\PerMachinePkg.wixproj" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/Bundle.wxs b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/Bundle.wxs
new file mode 100644
index 000000000..22879ee1a
--- /dev/null
+++ b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/Bundle.wxs
@@ -0,0 +1,13 @@
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:bal="http://wixtoolset.org/schemas/v4/wxs/bal">
+  <Bundle Id="PerMachineBundle" Name="PerMachineBundle" Manufacturer="Acme" Version="1.0.0.0">
+    <BootstrapperApplication>
+      <bal:WixStandardBootstrapperApplication LicenseUrl="https://www.example.com/license" Theme="hyperlinkLicense" />
+    </BootstrapperApplication>
+
+    <Variable Name="TestBundleId" Value="PerMachineBundleWix6 v1.0.0.0" />
+
+    <Chain>
+      <MsiPackage SourceFile="PerMachinePkgWix6.msi" />
+    </Chain>
+  </Bundle>
+</Wix>
diff --git a/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/PerMachineBundleWix6.wixproj b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/PerMachineBundleWix6.wixproj
new file mode 100644
index 000000000..bec8209e7
--- /dev/null
+++ b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachineBundleWix6/PerMachineBundleWix6.wixproj
@@ -0,0 +1,12 @@
+<Project Sdk="WixToolset.Sdk/6.0.2">
+  <PropertyGroup>
+    <ManagePackageVersionsCentrally>false</ManagePackageVersionsCentrally>
+    <OutputType>Bundle</OutputType>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="WixToolset.BootstrapperApplications.wixext" Version="6.0.2" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\PerMachinePkgWix6\PerMachinePkgWix6.wixproj" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/PerMachinePkgWix6.wixproj b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/PerMachinePkgWix6.wixproj
new file mode 100644
index 000000000..9fa921ec4
--- /dev/null
+++ b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/PerMachinePkgWix6.wixproj
@@ -0,0 +1,5 @@
+<Project Sdk="WixToolset.Sdk/6.0.2">
+  <PropertyGroup>
+    <ManagePackageVersionsCentrally>false</ManagePackageVersionsCentrally>
+  </PropertyGroup>
+</Project>
\ No newline at end of file
diff --git a/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/product.wxs b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/product.wxs
new file mode 100644
index 000000000..4b14c9d24
--- /dev/null
+++ b/src/test/burn/TestData6/ConfigurableScopeTests/PerMachinePkgWix6/product.wxs
@@ -0,0 +1,6 @@
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+  <Package Id="PerMachinePkg" Name="PerMachinePkg" Language="1033" Version="1.0.0.0" Manufacturer="Acme" Scope="perMachine">
+    <MediaTemplate EmbedCab="yes" />
+    <File Source="$(sys.SOURCEFILEPATH)" />
+  </Package>
+</Wix>
diff --git a/src/test/burn/TestData6/TestData6.proj b/src/test/burn/TestData6/TestData6.proj
new file mode 100644
index 000000000..6eeb18fdf
--- /dev/null
+++ b/src/test/burn/TestData6/TestData6.proj
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information. -->
+
+<Project Sdk="Microsoft.Build.Traversal">
+  <ItemGroup>
+    <ProjectReference Include="**\*.wixproj" />
+  </ItemGroup>
+</Project>
diff --git a/src/test/burn/TestData6/nuget.config b/src/test/burn/TestData6/nuget.config
new file mode 100644
index 000000000..ec40f2b20
--- /dev/null
+++ b/src/test/burn/TestData6/nuget.config
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+  </packageSources>
+
+  <packageSourceMapping>
+    <packageSource key="nuget.org">
+      <package pattern="WixToolset.*" />
+      <package pattern="*" />
+    </packageSource>
+  </packageSourceMapping>
+</configuration>
diff --git a/src/test/burn/WixToolsetTest.BurnE2E/ConfigurableScopeTests.cs b/src/test/burn/WixToolsetTest.BurnE2E/ConfigurableScopeTests.cs
index 9e8870fc1..8dc9c8204 100644
--- a/src/test/burn/WixToolsetTest.BurnE2E/ConfigurableScopeTests.cs
+++ b/src/test/burn/WixToolsetTest.BurnE2E/ConfigurableScopeTests.cs
@@ -150,6 +150,46 @@ public void BundleUpgradeWithSameScopeSucceeds()
             bundle.VerifyUnregisteredAndRemovedFromPackageCache(plannedPerMachine: false);
         }
 
+        [RuntimeFact]
+        public void BundleUpgradeFromWix6IsLockedToFirstBundlesScope()
+        {
+            var bundle = this.CreateBundleInstaller("PerMachineBundleWix6");
+            bundle.Install();
+
+            bundle.VerifyRegisteredAndInPackageCache(plannedPerMachine: true);
+
+            var testBAController = this.CreateTestBAController();
+            testBAController.SetBundleScope(BundleScope.PerUser);
+
+            var bundleV2 = this.CreateBundleInstaller("PerMachineBundleV2");
+            var log = bundleV2.Install();
+            Assert.True(LogVerifier.MessageInLogFileRegex(log, @"Upgraded bundle [{][0-9A-Fa-f\-]{36}[}] was already installed with scope: PerMachine\. Scope cannot change during upgrade\."));
+
+            bundleV2.Uninstall();
+            bundleV2.VerifyUnregisteredAndRemovedFromPackageCache(plannedPerMachine: true);
+            bundle.VerifyUnregisteredAndRemovedFromPackageCache(plannedPerMachine: true);
+        }
+
+        [RuntimeFact]
+        public void BundleUpgradeFromWix6WithSameScopeSucceeds()
+        {
+            var bundle = this.CreateBundleInstaller("PerMachineBundleWix6");
+            bundle.Install();
+
+            bundle.VerifyRegisteredAndInPackageCache(plannedPerMachine: true);
+
+            var testBAController = this.CreateTestBAController();
+            testBAController.SetBundleScope(BundleScope.PerMachine);
+
+            var bundleV2 = this.CreateBundleInstaller("PerMachineBundleV2");
+            var log = bundleV2.Install();
+            Assert.True(LogVerifier.MessageInLogFileRegex(log, @"Upgraded bundle [{][0-9A-Fa-f\-]{36}[}] was already installed with scope: PerMachine\. Scope cannot change during upgrade\."));
+
+            bundleV2.Uninstall();
+            bundleV2.VerifyUnregisteredAndRemovedFromPackageCache(plannedPerMachine: true);
+            bundle.VerifyUnregisteredAndRemovedFromPackageCache(plannedPerMachine: true);
+        }
+
         [RuntimeFact]
         public void PMOU_Bundle_Default_Plan_Installs_PerMachine()
         {
diff --git a/src/test/burn/test_burn.cmd b/src/test/burn/test_burn.cmd
index a956c8384..3f03216b5 100644
--- a/src/test/burn/test_burn.cmd
+++ b/src/test/burn/test_burn.cmd
@@ -15,6 +15,7 @@
 
 msbuild -Restore -p:Configuration=%_C% -tl -nologo -m -warnaserror -bl:%_L%\test_burn_build.binlog || exit /b
 msbuild -Restore TestData\TestData.proj -p:Configuration=%_C% -tl -nologo -m -warnaserror -bl:%_L%\test_burn_data_build.binlog || exit /b
+msbuild -Restore TestData6\TestData6.proj -p:Configuration=%_C% -tl -nologo -m -warnaserror -bl:%_L%\test_burn_data6_build.binlog || exit /b
 
 "%_B%\net462\win-x86\testexe.exe" /dm "%_B%\net8.0-windows\testhost.exe"
 mt.exe -manifest "WixToolsetTest.BurnE2E\testhost.longpathaware.manifest" -updateresource:"%_B%\net8.0-windows\testhost.exe"