diff --git a/FSharpBuild.Directory.Build.props b/FSharpBuild.Directory.Build.props
index a1ba7ab156d..95036cb5ae1 100644
--- a/FSharpBuild.Directory.Build.props
+++ b/FSharpBuild.Directory.Build.props
@@ -92,6 +92,7 @@
     <MicroBuildAssemblyFileLanguage>fs</MicroBuildAssemblyFileLanguage>
     <UseStandardResourceNames>false</UseStandardResourceNames>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <FSharpCoreProtoVersion>4.6.2</FSharpCoreProtoVersion>
   </PropertyGroup>
 
   <!-- SDK targets override -->
diff --git a/eng/build-utils.ps1 b/eng/build-utils.ps1
index d1e5dd85d55..a1e16a5f7ec 100644
--- a/eng/build-utils.ps1
+++ b/eng/build-utils.ps1
@@ -249,7 +249,7 @@ function Make-BootstrapBuild() {
     $projectPath = "$RepoRoot\proto.proj"
     Run-MSBuild $projectPath "/restore /t:Build" -logFileName "Bootstrap" -configuration $bootstrapConfiguration
     Copy-Item "$ArtifactsDir\bin\fsc\$bootstrapConfiguration\$bootstrapTfm\*" -Destination $dir
-    Copy-Item "$ArtifactsDir\bin\fsi\$bootstrapConfiguration\$bootstrapTfm\*" -Destination $dir
+    Copy-Item "$ArtifactsDir\bin\fsi\$bootstrapConfiguration\$bootstrapTfm\*" -Destination $dir -Force
 
     return $dir
 }
diff --git a/src/fsharp/FSharp.Build/FSharp.Build.fsproj b/src/fsharp/FSharp.Build/FSharp.Build.fsproj
index 0dad55058b0..38a1ffa90bc 100644
--- a/src/fsharp/FSharp.Build/FSharp.Build.fsproj
+++ b/src/fsharp/FSharp.Build/FSharp.Build.fsproj
@@ -33,7 +33,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net472'">
diff --git a/src/fsharp/FSharp.Compiler.Interactive.Settings/FSharp.Compiler.Interactive.Settings.fsproj b/src/fsharp/FSharp.Compiler.Interactive.Settings/FSharp.Compiler.Interactive.Settings.fsproj
index 6307f17baf3..51c4017d67d 100644
--- a/src/fsharp/FSharp.Compiler.Interactive.Settings/FSharp.Compiler.Interactive.Settings.fsproj
+++ b/src/fsharp/FSharp.Compiler.Interactive.Settings/FSharp.Compiler.Interactive.Settings.fsproj
@@ -28,7 +28,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj b/src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj
index 9fef6d27589..f7d8f20440a 100644
--- a/src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj
+++ b/src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj
@@ -675,7 +675,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net472'">
diff --git a/src/fsharp/FSharp.Compiler.Server.Shared/FSharp.Compiler.Server.Shared.fsproj b/src/fsharp/FSharp.Compiler.Server.Shared/FSharp.Compiler.Server.Shared.fsproj
index 75a7353bb96..faab0f8cc3b 100644
--- a/src/fsharp/FSharp.Compiler.Server.Shared/FSharp.Compiler.Server.Shared.fsproj
+++ b/src/fsharp/FSharp.Compiler.Server.Shared/FSharp.Compiler.Server.Shared.fsproj
@@ -21,7 +21,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.csproj b/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.csproj
index fd2d5162c75..e304369556b 100644
--- a/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.csproj
+++ b/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.csproj
@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj">
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
     </ProjectReference>
   </ItemGroup>
diff --git a/src/fsharp/FSharp.Core/FSharp.Core.fsproj b/src/fsharp/FSharp.Core/FSharp.Core.fsproj
index 440850ed55c..b3ed7590476 100644
--- a/src/fsharp/FSharp.Core/FSharp.Core.fsproj
+++ b/src/fsharp/FSharp.Core/FSharp.Core.fsproj
@@ -232,7 +232,7 @@
   <!-- NOTE: The optdata and sigdata files are no longer needed by the F# compiler (the information is -->
   <!-- integrated as resources into more recent FSharp.Core.dll's. However they are still produced to -->
   <!-- allow older versions of the F# compiler to reference more recent FSharp.Core packages -->
-  <Target Name="CopyToBuiltBin" BeforeTargets="AfterCompile" AfterTargets="CoreCompile" >
+  <Target Name="CopyToBuiltBin" BeforeTargets="AfterCompile" AfterTargets="CoreCompile" Condition="'$(Configuration)' != 'Proto'" >
     <ItemGroup>
       <BuiltProjectOutputGroupKeyOutput Include="$(IntermediateOutputPath)\FSharp.Core.sigdata" />
       <BuiltProjectOutputGroupKeyOutput Include="$(IntermediateOutputPath)\FSharp.Core.optdata" />
diff --git a/src/fsharp/fsc/fsc.fsproj b/src/fsharp/fsc/fsc.fsproj
index 8ddb082c56a..8ea9e6d8b07 100644
--- a/src/fsharp/fsc/fsc.fsproj
+++ b/src/fsharp/fsc/fsc.fsproj
@@ -29,7 +29,12 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
+  </ItemGroup>
+
+  <ItemGroup>
     <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Build\FSharp.Build.fsproj" />
     <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
   </ItemGroup>
diff --git a/src/fsharp/fsi/fsi.fsproj b/src/fsharp/fsi/fsi.fsproj
index a7bafddfded..d088ca69384 100644
--- a/src/fsharp/fsi/fsi.fsproj
+++ b/src/fsharp/fsi/fsi.fsproj
@@ -26,12 +26,17 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
-    <ProjectReference Include="..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
-    <ProjectReference Include="..\FSharp.Compiler.Interactive.Settings\FSharp.Compiler.Interactive.Settings.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Interactive.Settings\FSharp.Compiler.Interactive.Settings.fsproj" />
 
     <!-- only used when '$(TargetFramework)' == 'net472' -->
-    <ProjectReference Include="..\FSharp.Compiler.Server.Shared\FSharp.Compiler.Server.Shared.fsproj" Condition="'$(TargetFramework)' == 'net472'" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Server.Shared\FSharp.Compiler.Server.Shared.fsproj" Condition="'$(TargetFramework)' == 'net472'" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net472'">
diff --git a/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj b/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
index dbe31f6ec2a..96117f719f4 100644
--- a/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
+++ b/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
@@ -26,10 +26,15 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
-    <ProjectReference Include="..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
-    <ProjectReference Include="..\FSharp.Compiler.Interactive.Settings\FSharp.Compiler.Interactive.Settings.fsproj" />
-    <ProjectReference Include="..\FSharp.Compiler.Server.Shared\FSharp.Compiler.Server.Shared.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Interactive.Settings\FSharp.Compiler.Interactive.Settings.fsproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Server.Shared\FSharp.Compiler.Server.Shared.fsproj" />
   </ItemGroup>
 
   <ItemGroup>