Problem using NASM on Visual Studio target (CMake v3.7)

I'm adding NASM assembly files with:

enable_language(ASM_NASM)
...
add_library(test STATIC rdrand-x86_64.asm)

The NASM assembler is found, but the target generates the following vcxproj entries:

  <ItemGroup>
    <None Include="....\test\rdrand-x86_64.asm" />
  </ItemGroup>

Note the None element, which just includes the asm file into the test target, but nothing is compiled.