diff --git a/lib/load-cabal-plan.nix b/lib/load-cabal-plan.nix
index adf3a6898d..2c9ac23867 100644
--- a/lib/load-cabal-plan.nix
+++ b/lib/load-cabal-plan.nix
@@ -5,6 +5,12 @@ let
   plan-json = builtins.fromJSON (
     builtins.unsafeDiscardStringContext (
       builtins.readFile (callProjectResults.projectNix + "/plan.json")));
+  # Function to add context back to the strings we get from `plan.json`
+  addContext = s:
+    let storeDirMatch = builtins.match ".*(${builtins.storeDir}/[^/]+).*" s;
+    in if storeDirMatch == null
+      then s
+      else builtins.appendContext s { ${builtins.head storeDirMatch} = { path = true; }; };
   # All the units in the plan indexed by unit ID.
   by-id = pkgs.lib.listToAttrs (map (x: { name = x.id; value = x; }) plan-json.install-plan);
   # Find the names of all the pre-existing packages used by a list of dependencies
@@ -104,7 +110,9 @@ in {
                   + pkgs.lib.optionalString (p.pkg-src.source-repo.subdir != ".") "/${p.pkg-src.source-repo.subdir}";
               } // pkgs.lib.optionalAttrs (p.pkg-src.type or "" == "repo-tar") {
                 src = pkgs.lib.mkDefault (pkgs.fetchurl {
-                  url = p.pkg-src.repo.uri + "${pkgs.lib.optionalString (!pkgs.lib.hasSuffix "/" p.pkg-src.repo.uri) "/"}package/${p.pkg-name}-${p.pkg-version}.tar.gz";
+                   # repo.uri might look like file:/nix/store/xxx; using addContext, we let nix know about the dependency on
+                   # /nix/store/xxx.  Otherwise we can run into the situation where nix won't be able to access the dependencies needed to build. (e.g. the /nix/store/xxx path).
+                  url = addContext p.pkg-src.repo.uri + "${pkgs.lib.optionalString (!pkgs.lib.hasSuffix "/" p.pkg-src.repo.uri) "/"}package/${p.pkg-name}-${p.pkg-version}.tar.gz";
                   sha256 = p.pkg-src-sha256;
                 });
               } // pkgs.lib.optionalAttrs (cabal2nix ? package-description-override && p.pkg-version == cabal2nix.package.identifier.version) {
diff --git a/test/cabal.project.local b/test/cabal.project.local
index db3a1f6521..e3bba2b48f 100644
--- a/test/cabal.project.local
+++ b/test/cabal.project.local
@@ -24,14 +24,14 @@ repository head.hackage.ghc.haskell.org
      f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89
      26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
      7541f32a4ccca4f97aea3b22f5e593ba2c0267546016b992dfadcd2fe944e55d
-  --sha256: sha256-VFRuIfs3k6nyLVvT445wFRDy+bpcy1LVmLCMg1Oo/uE=
+  --sha256: sha256-Z6cqRAlbV1WNbK4fKdcWHQcLA8CGpzfnTOd8QxcOy+c=
 
 repository ghcjs-overlay
-  url: https://raw.githubusercontent.com/input-output-hk/hackage-overlay-ghcjs/01ecad22c0a72e3c5a49262357cf0b062892d87f
+  url: https://raw.githubusercontent.com/input-output-hk/hackage-overlay-ghcjs/56cd424e8529e7a1fc29c6126abdc66f09467306
   secure: True
   root-keys:
   key-threshold: 0
-  --sha256: sha256-BjyXYh6oS4wE1iHlY/7as7vkmjxFOXzK6nOYzbzjQrM=
+  --sha256: sha256-nU0/HKy4Om1GohCcU+gUWCDPgyclYdFzAgzfXe0tgf0=
 
 if os(ghcjs)
   extra-packages: ghci