NuGet packing same dll twice in different folders: Cannot add part for the specified URI because it is already in the package

Question

I have the following two lines in my nuspec which result in the error:

Cannot add part for the specified URI because it is already in the package.

Here's the code in the nuspec:

        <file src="bin\release\*.dll" target="lib" />
        <file src="..\myProj\bin\release\*.dll" target="tools" />

Any thoughts on how I can get the same dlls into both targets? I'm using VSTS to do the nuget packaging. (I wasn't able to find any similar questions.)