Happy version downgrade

Friends I can't build ghc-9.0 because of this: checking for ghc-pkg matching /opt/ghc/bin/ghc... /opt/ghc/bin/ghc-pkg checking for happy... /home/simonpj/.cabal/bin/happy checking for version of happy... 1.20.0 configure: error: Happy version 1.19 is required to compile GHC. What is the easiest way to fix? I have happy 1.19.8, but it's not called plain "happy" bash$ happy-1.19.8 --version Happy Version 1.19.8 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. Thanks Simon