diff --git a/third_party/nixpkgs-exposed/exposed/default.nix b/third_party/nixpkgs-exposed/exposed/default.nix
index 3d3e23afa..478b55cb2 100644
--- a/third_party/nixpkgs-exposed/exposed/default.nix
+++ b/third_party/nixpkgs-exposed/exposed/default.nix
@@ -190,7 +190,9 @@
     ;
 
   haskellPackages = (nixpkgs.haskellPackages.override {
-    overrides = (import ../haskell_overlay { pkgs = nixpkgs; });
+    overrides = (import ../../overlays/haskell
+    { /* empty readTree arg */ }
+    { pkgs = nixpkgs; });
   });
 
   gradle_6 = (nixpkgs.gradleGen.override {
diff --git a/third_party/nixpkgs-exposed/haskell_overlay/default.nix b/third_party/overlays/haskell/default.nix
similarity index 79%
rename from third_party/nixpkgs-exposed/haskell_overlay/default.nix
rename to third_party/overlays/haskell/default.nix
index 9b025d7d2..975918803 100644
--- a/third_party/nixpkgs-exposed/haskell_overlay/default.nix
+++ b/third_party/overlays/haskell/default.nix
@@ -1,4 +1,8 @@
-{ pkgs }:
+# Defines overrides for Haskell packages, for example to avoid
+# breakage currently present in nixpkgs or to modify package versions.
+
+{ ... }: # This file needs nothing from readTree
+{ pkgs }: # ... but is called with a separate package set in the overlay
 
 self: super: with pkgs.haskell.lib; rec {
   generic-arbitrary = appendPatch
diff --git a/third_party/nixpkgs-exposed/haskell_overlay/patches/generic-arbitrary-export-garbitrary.patch b/third_party/overlays/haskell/patches/generic-arbitrary-export-garbitrary.patch
similarity index 100%
rename from third_party/nixpkgs-exposed/haskell_overlay/patches/generic-arbitrary-export-garbitrary.patch
rename to third_party/overlays/haskell/patches/generic-arbitrary-export-garbitrary.patch