You’re probably reading an old document - this restriction was removed with the introduction of roles. https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_

You’re probably reading an old document - this restriction was removed with the introduction of roles. https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/safe-haskell.html https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_gui... Roles were introduced in 7.8.something, and GND was added to Safe.