diff --git a/proprietary/DiskImage/Duplicati.Proprietary.DiskImage.csproj b/proprietary/DiskImage/Duplicati.Proprietary.DiskImage.csproj
index 2b4718149..470c66803 100644
--- a/proprietary/DiskImage/Duplicati.Proprietary.DiskImage.csproj
+++ b/proprietary/DiskImage/Duplicati.Proprietary.DiskImage.csproj
@@ -39,4 +39,9 @@
     </ContentWithTargetPath>
   </ItemGroup>
 
+  <!-- Allow the Unit tests to be able to see internal types. -->
+  <ItemGroup>
+    <InternalsVisibleTo Include="Duplicati.UnitTest" />
+  </ItemGroup>
+
 </Project>