1. Build and install OOS VSIX from https://github.com/Microsoft/visualfsharp/pull/3328 2. Check out https://github.com/Microsoft/visualfsharp/pull/3330 3. Try to build it in VS 4. Result > E:\github\visualfsharp\Proto\net40\bin\Microsoft.FSharp-proto.targets(224,9): error MSB6006: "fsc-proto.exe" exited with code -1073741819.