diff --git a/pkgs/development/libraries/agda/agda2hs-base/default.nix b/pkgs/development/libraries/agda/agda2hs-base/default.nix
index 97a3b6de4809..eb034878a51d 100644
--- a/pkgs/development/libraries/agda/agda2hs-base/default.nix
+++ b/pkgs/development/libraries/agda/agda2hs-base/default.nix
@@ -9,7 +9,9 @@ mkDerivation {
 
   inherit (haskellPackages.agda2hs) src version;
 
-  sourceRoot = "source/lib/base";
+  postUnpack = ''
+    sourceRoot="$sourceRoot/lib/base"
+  '';
 
   libraryFile = "base.agda-lib";