-XGeneralizedNewtypeDeriving is not allowed in Safe Haskell

This happens both in GHC 7.8 and GHC 7.10.

I thought I remembered reading somewhere that GNTD is now part of the safe language?  The GHC manual used to state that GNTD is not allowed in Safe Haskell:

https://downloads.haskell.org/~ghc/7.6.3/docs/html/users_guide/safe-haskell.html#safe-language

But this language on GNTD not being part of the safe language was removed in the 7.8 manual:

https://downloads.haskell.org/~ghc/7.8.2/docs/html/users_guide/safe-haskell.html#safe-language

The GHC release notes don't say anything about this one way or the other.  Thoughts?