diff --git a/flake.lock b/flake.lock
index 03b81be2a..835fddc39 100644
--- a/flake.lock
+++ b/flake.lock
@@ -120,11 +120,11 @@
     "hackage": {
       "flake": false,
       "locked": {
-        "lastModified": 1750292855,
-        "narHash": "sha256-fI06UmPtWs+lZy6aKE4nBKDWRKJeJr8s+qUAQgvpwCM=",
+        "lastModified": 1750307553,
+        "narHash": "sha256-iiafNoeLHwlSLQTyvy8nPe2t6g5AV4PPcpMeH/2/DLs=",
         "owner": "input-output-hk",
         "repo": "hackage.nix",
-        "rev": "87d047843ca7b233a428e550c68e6b5faaaa8008",
+        "rev": "f7867baa8817fab296528f4a4ec39d1c7c4da4f3",
         "type": "github"
       },
       "original": {
@@ -150,6 +150,22 @@
         "type": "github"
       }
     },
+    "hackage-internal": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1750307553,
+        "narHash": "sha256-iiafNoeLHwlSLQTyvy8nPe2t6g5AV4PPcpMeH/2/DLs=",
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "rev": "f7867baa8817fab296528f4a4ec39d1c7c4da4f3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "input-output-hk",
+        "repo": "hackage.nix",
+        "type": "github"
+      }
+    },
     "hls": {
       "flake": false,
       "locked": {
@@ -527,6 +543,7 @@
         "ghc-8.6.5-iohk": "ghc-8.6.5-iohk",
         "hackage": "hackage",
         "hackage-for-stackage": "hackage-for-stackage",
+        "hackage-internal": "hackage-internal",
         "hls": "hls",
         "hls-1.10": "hls-1.10",
         "hls-2.0": "hls-2.0",
diff --git a/flake.nix b/flake.nix
index a28bd6abb..54723b2b8 100644
--- a/flake.nix
+++ b/flake.nix
@@ -31,6 +31,10 @@
       url = "github:input-output-hk/hackage.nix/for-stackage";
       flake = false;
     };
+    hackage-internal = {
+      url = "github:input-output-hk/hackage.nix";
+      flake = false;
+    };
     stackage = {
       url = "github:input-output-hk/stackage.nix";
       flake = false;
diff --git a/overlays/haskell.nix b/overlays/haskell.nix
index 01a15ecdc..1f3b46861 100644
--- a/overlays/haskell.nix
+++ b/overlays/haskell.nix
@@ -437,8 +437,8 @@ final: prev: {
         # If you want to update this value it important to check the
         # materializations.  Turn `checkMaterialization` on below and
         # check the CI results before turning it off again.
-        internalHackageIndexState = "2024-10-17T00:00:00Z"; # Remember to also update ../nix-tools/cabal.project and ../nix-tools/flake.lock
-
+        internalHackageIndexState = builtins.head (builtins.attrNames (
+          import (sources.hackage-internal + "/index-state.nix")));
         checkMaterialization = false; # This is the default. Use an overlay to set it to true and test all the materialized files
 
         # Helps materialize the output of derivations
@@ -601,7 +601,13 @@ final: prev: {
         # Takes a haskell src directory runs cabal new-configure and plan-to-nix.
         # Resulting nix files are added to nix-plan subdirectory.
         callCabalProjectToNix = import ../lib/call-cabal-project-to-nix.nix {
-            index-state-hashes = import indexStateHashesPath;
+            index-state-hashes =
+              (
+                if builtins.pathExists (hackageSrc + "/index-state.nix")
+                  then import (hackageSrc + "/index-state.nix")
+                  else import (hackageSrc + "/index-state-hashes.nix")
+              )
+              // import (sources.hackage-internal + "/index-state.nix");
             inherit (final.buildPackages.haskell-nix) haskellLib;
             pkgs = final.buildPackages.pkgs;
             inherit (final.buildPackages.pkgs) cacert;