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/src/fsharp/FSharp.Build/FSharp.Build.fsproj b/src/fsharp/FSharp.Build/FSharp.Build.fsproj
index 0dad55058b0..7bab41796bd 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="..\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..799fda75246 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="'$(Configuration)' != 'Proto'" Include="..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(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..bed8c55e91e 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="..\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..39ba868aeee 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="'$(Configuration)' != 'Proto'" Include="..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/fsharp/fsc/fsc.fsproj b/src/fsharp/fsc/fsc.fsproj
index 8ddb082c56a..4b812970716 100644
--- a/src/fsharp/fsc/fsc.fsproj
+++ b/src/fsharp/fsc/fsc.fsproj
@@ -29,9 +29,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Core\FSharp.Core.fsproj" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Build\FSharp.Build.fsproj" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="..\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/fsi/fsi.fsproj b/src/fsharp/fsi/fsi.fsproj
index a7bafddfded..43e95426220 100644
--- a/src/fsharp/fsi/fsi.fsproj
+++ b/src/fsharp/fsi/fsi.fsproj
@@ -26,7 +26,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
     <ProjectReference Include="..\FSharp.Compiler.Private\FSharp.Compiler.Private.fsproj" />
     <ProjectReference Include="..\FSharp.Compiler.Interactive.Settings\FSharp.Compiler.Interactive.Settings.fsproj" />
 
diff --git a/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj b/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
index dbe31f6ec2a..fd6c5b7ef3e 100644
--- a/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
+++ b/src/fsharp/fsiAnyCpu/fsiAnyCpu.fsproj
@@ -26,7 +26,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Condition="'$(Configuration)' != 'Proto'" Include="..\FSharp.Core\FSharp.Core.fsproj" />
+     <!-- when building the proto tools, use an FSharp.Core package - the latest FSharp.Core code may not build with the LKG compiler -->
+    <PackageReference Condition="'$(Configuration)' == 'Proto'" Include="FSharp.Core" Version="$(FSharpCoreProtoVersion)" />
     <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" />