diff --git a/nix/haskell.nix b/nix/haskell.nix
index 6f8dfb21..bf4e3206 100644
--- a/nix/haskell.nix
+++ b/nix/haskell.nix
@@ -25,6 +25,13 @@ let
     ghc = buildPackages.haskell-nix.compiler.${compiler};
   } // {
     inherit src;
+    pkg-def-extras = [
+      (hackage: {
+        packages = {
+          "async-timer" = hackage."async-timer"."0.2.0.0".revisions.default;
+        };
+      })
+    ];
     modules = [
       { compiler.nix-name = compiler; }