I have problems with validating my changes in template-haskell, file Language/Haskell/Th/Syntax.hs. I added isTrue# function in the import: import GHC.Base ( Int(..), Int#, (<#), (==#), isTrue# ) And later on I'm using isTrue#. However, when stage1 compiler tries to compile Syntax.hs, validation fails (due to -Werror): libraries/template-haskell/Language/Haskell/TH/Syntax.hs:19:1: Warning: The import of ‛Int#, Int, ==#, <#’ from module ‛GHC.Base’ is redundant The module obviously uses mentioned operators and data types. I wonder what did I miss. Ideas anyone? Janek