diff --git a/pkgs/build-support/cabal/default.nix b/pkgs/build-support/cabal/default.nix
index 6ede3f56923..d57afb7bf9d 100644
--- a/pkgs/build-support/cabal/default.nix
+++ b/pkgs/build-support/cabal/default.nix
@@ -147,7 +147,11 @@ assert enableCheckPhase -> stdenv.lib.versionOlder "7" ghc.ghcVersion;
               ./Setup build
 
               export GHC_PACKAGE_PATH=$(${ghc.GHCPackages})
-              [ -n "$noHaddock" ] || ./Setup haddock
+              if [ -n "$noHaddock" ]; then
+                export LANG="en_US.UTF-8"
+                ./Setup haddock
+                unset LANG
+              fi
 
               eval "$postBuild"
             '';