diff --git a/flake.nix b/flake.nix
index a9c487c211..c6987f54d5 100644
--- a/flake.nix
+++ b/flake.nix
@@ -66,7 +66,13 @@
           inputMap = {
             "https://input-output-hk.github.io/cardano-haskell-packages" = inputs.CHaP;
           };
-
+          # Also currently needed to make `nix flake lock --update-input CHaP` work.
+          cabalProjectLocal = ''
+            repository cardano-haskell-packages-local
+              url: file:${inputs.CHaP}
+              secure: True
+            active-repositories: hackage.haskell.org, cardano-haskell-packages-local
+          '';
           # tools we want in our shell, from hackage
           shell.tools =
             {
@@ -117,6 +123,7 @@
           );
       in
         nixpkgs.lib.recursiveUpdate flake rec {
+          project = cabalProject;
           # add a required job, that's basically all hydraJobs.
           hydraJobs =
             nixpkgs.callPackages inputs.iohkNix.utils.ciJobsAggregates