diff --git a/lib/call-cabal-project-to-nix.nix b/lib/call-cabal-project-to-nix.nix
index 6996ba945b..2f5cfe7bc8 100644
--- a/lib/call-cabal-project-to-nix.nix
+++ b/lib/call-cabal-project-to-nix.nix
@@ -165,7 +165,10 @@ let
         --with-ghc-pkg=${ghc.targetPrefix}ghc-pkg \
         --enable-tests
 
-    export LANG=C.utf8 # Needed or stack-to-nix will die on unicode inputs
+    # Needed or stack-to-nix will die on unicode inputs
+    export LANG = "en_US.UTF-8";
+    export LC_ALL = "en_US.UTF-8";
+
     mkdir -p $out
 
     # ensure we have all our .cabal files (also those generated from package.yaml) files.
diff --git a/lib/call-stack-to-nix.nix b/lib/call-stack-to-nix.nix
index 1c12e13ee7..ed3d95ff1e 100644
--- a/lib/call-stack-to-nix.nix
+++ b/lib/call-stack-to-nix.nix
@@ -17,7 +17,9 @@ let
   stack = runCommand "stack-to-nix-pkgs" {
     nativeBuildInputs = [ nix-tools pkgs.nix-prefetch-git pkgs.cacert ];
   } (''
-    export LANG=C.utf8 # Needed or stack-to-nix will die on unicode inputs
+    # Needed or stack-to-nix will die on unicode inputs
+    export LANG = "en_US.UTF-8";
+    export LC_ALL = "en_US.UTF-8";
     mkdir -p $out
   '' + pkgs.lib.optionalString (cache != null) ''
     cp ${mkCacheFile cache} $out/.stack-to-nix.cache
diff --git a/overlays/haskell.nix b/overlays/haskell.nix
index 42ae766ff3..e022e7ca53 100644
--- a/overlays/haskell.nix
+++ b/overlays/haskell.nix
@@ -198,7 +198,8 @@ self: super: {
             self.buildPackages.pkgs.runCommand "${name}.nix" {
                 nativeBuildInputs = [ self.buildPackages.haskell-nix.nix-tools ];
             } ''
-            export LANG=C.utf8 # Needed or cabal-to-nix will die on unicode inputs
+            export LANG = "en_US.UTF-8";
+            export LC_ALL = "en_US.UTF-8";
             cabal-to-nix "${src}" "${src}/${cabal-file}" > "$out"
             '';