diff --git a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
index cdbc943f47..3a3b97c08a 100644
--- a/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
+++ b/BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj
@@ -222,6 +222,7 @@
     <Compile Include="Computers\Commodore64\Cassette\CassettePortDevice.cs" />
     <Compile Include="Computers\Commodore64\Cassette\TapeDrive.cs" />
     <Compile Include="Computers\Commodore64\C64FormatFinder.cs" />
+    <Compile Include="Computers\Commodore64\Media\DiskBuilder.cs" />
     <Compile Include="Computers\Commodore64\Media\Tape.cs" />
     <Compile Include="Computers\Commodore64\Media\PRG.cs" />
     <Compile Include="Computers\Commodore64\Cartridge\CartridgeDevice.cs" />