diff --git a/src/buildtools/fslex/fslex.fsproj b/src/buildtools/fslex/fslex.fsproj
index 64d34426053..2766098c25d 100644
--- a/src/buildtools/fslex/fslex.fsproj
+++ b/src/buildtools/fslex/fslex.fsproj
@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <DefineConstants>INTERNALIZED_FSLEXYACC_RUNTIME;$(DefineConstant)</DefineConstants>
+    <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
   </PropertyGroup>
 
   <ItemGroup>
@@ -19,4 +20,8 @@
     <Compile Include="fslex.fs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\..\fsharp\FSharp.Core\FSharp.Core.fsproj" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/buildtools/fsyacc/fsyacc.fsproj b/src/buildtools/fsyacc/fsyacc.fsproj
index 693080ec985..dc5a4f67f36 100644
--- a/src/buildtools/fsyacc/fsyacc.fsproj
+++ b/src/buildtools/fsyacc/fsyacc.fsproj
@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <DefineConstants>INTERNALIZED_FSLEXYACC_RUNTIME;$(DefineConstant)</DefineConstants>
+    <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
   </PropertyGroup>
 
   <ItemGroup>
@@ -19,4 +20,8 @@
     <Compile Include="fsyacc.fs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="$(MSBuildThisFileDirectory)..\..\fsharp\FSharp.Core\FSharp.Core.fsproj" />
+  </ItemGroup>
+
 </Project>