SMP-related build failure on GHC 8.4-alpha1

[deepfire]

Build fails on 8.4.1-alpha1:

[3 of 7] Compiling Text.XML.Stream.Render ( Text/XML/Stream/Render.hs, dist/build/Text/XML/Stream/Render.o )

Text/XML/Stream/Render.hs:405:10: error:
    • No instance for (Semigroup Attributes)
        arising from the superclasses of an instance declaration
    • In the instance declaration for ‘Monoid Attributes’
    |
405 | instance Monoid Attributes where
    |          ^^^^^^^^^^^^^^^^^
builder for ‘/nix/store/4q1nmhiclmk8h1j0w71ci4j0fzysliyr-xml-conduit-1.7.0.1.drv’ failed with exit code 1