diff --git a/pkgs/applications/science/biology/mrtrix/default.nix b/pkgs/applications/science/biology/mrtrix/default.nix
index ef8c738055fc..b098cd354ba5 100644
--- a/pkgs/applications/science/biology/mrtrix/default.nix
+++ b/pkgs/applications/science/biology/mrtrix/default.nix
@@ -4,7 +4,7 @@
   fetchFromGitHub,
   python,
   makeWrapper,
-  eigen,
+  eigen_3_4_0,
   fftw,
   libtiff,
   libpng,
@@ -18,41 +18,8 @@
   libXext,
   less,
   withGui ? true,
-  fetchFromGitLab,
-  fetchpatch,
 }:
 
-let
-  # reverts 'eigen: 3.4.0 -> 3.4.0-unstable-2022-05-19'
-  # https://github.com/NixOS/nixpkgs/commit/d298f046edabc84b56bd788e11eaf7ed72f8171c
-  eigen' = (
-    eigen.overrideAttrs (old: rec {
-      version = "3.4.0";
-      src = fetchFromGitLab {
-        owner = "libeigen";
-        repo = "eigen";
-        tag = version;
-        hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
-      };
-      patches = (old.patches or [ ]) ++ [
-        # Fixes e.g. onnxruntime on aarch64-darwin:
-        # https://hydra.nixos.org/build/248915128/nixlog/1,
-        # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
-        #
-        # The patch is from
-        # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
-        # which is two years old,
-        # but Eigen hasn't had a release in two years either:
-        # https://gitlab.com/libeigen/eigen/-/issues/2699.
-        (fetchpatch {
-          url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
-          hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
-        })
-      ];
-    })
-  );
-in
-
 stdenv.mkDerivation rec {
   pname = "mrtrix";
   version = "3.0.4-unstable-2025-04-09";
@@ -74,7 +41,7 @@ stdenv.mkDerivation rec {
   buildInputs =
     [
       ants
-      eigen'
+      eigen_3_4_0
       python
       fftw
       libtiff
@@ -113,7 +80,7 @@ stdenv.mkDerivation rec {
 
   configurePhase = ''
     runHook preConfigure
-    export EIGEN_CFLAGS="-isystem ${eigen'}/include/eigen3"
+    export EIGEN_CFLAGS="-isystem ${eigen_3_4_0}/include/eigen3"
     unset LD  # similar to https://github.com/MRtrix3/mrtrix3/issues/1519
     ./configure ${lib.optionalString (!withGui) "-nogui"};
     runHook postConfigure
diff --git a/pkgs/by-name/cu/curv/package.nix b/pkgs/by-name/cu/curv/package.nix
index 060efc4c84a4..2f63ddd9534f 100644
--- a/pkgs/by-name/cu/curv/package.nix
+++ b/pkgs/by-name/cu/curv/package.nix
@@ -2,13 +2,11 @@
   lib,
   stdenv,
   fetchFromGitea,
-  fetchFromGitLab,
-  fetchpatch,
   cmake,
   git,
   pkg-config,
   boost,
-  eigen,
+  eigen_3_4_0,
   glm,
   libGL,
   libpng,
@@ -43,33 +41,7 @@ stdenv.mkDerivation {
   buildInputs =
     [
       boost
-      # https://codeberg.org/doug-moen/curv/issues/228
-      # reverts 'eigen: 3.4.0 -> 3.4.0-unstable-2022-05-19'
-      # https://github.com/nixos/nixpkgs/commit/d298f046edabc84b56bd788e11eaf7ed72f8171c
-      (eigen.overrideAttrs (old: rec {
-        version = "3.4.0";
-        src = fetchFromGitLab {
-          owner = "libeigen";
-          repo = "eigen";
-          rev = version;
-          hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
-        };
-        patches = (old.patches or [ ]) ++ [
-          # Fixes e.g. onnxruntime on aarch64-darwin:
-          # https://hydra.nixos.org/build/248915128/nixlog/1,
-          # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
-          #
-          # The patch is from
-          # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
-          # which is two years old,
-          # but Eigen hasn't had a release in two years either:
-          # https://gitlab.com/libeigen/eigen/-/issues/2699.
-          (fetchpatch {
-            url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
-            hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
-          })
-        ];
-      }))
+      eigen_3_4_0
       glm
       libGL
       libpng
diff --git a/pkgs/by-name/ks/kstars/package.nix b/pkgs/by-name/ks/kstars/package.nix
index 69620c4ad5fc..4f48e54fedcc 100644
--- a/pkgs/by-name/ks/kstars/package.nix
+++ b/pkgs/by-name/ks/kstars/package.nix
@@ -2,12 +2,10 @@
   lib,
   stdenv,
   fetchurl,
-  fetchFromGitLab,
-  fetchpatch,
   cfitsio,
   cmake,
   curl,
-  eigen,
+  eigen_3_4_0,
   gsl,
   indi-full,
   kdePackages,
@@ -22,35 +20,6 @@
   zlib,
 }:
 
-let
-  # reverts 'eigen: 3.4.0 -> 3.4.0-unstable-2022-05-19'
-  # https://github.com/nixos/nixpkgs/commit/d298f046edabc84b56bd788e11eaf7ed72f8171c
-  eigen' = eigen.overrideAttrs (old: rec {
-    version = "3.4.0";
-    src = fetchFromGitLab {
-      owner = "libeigen";
-      repo = "eigen";
-      rev = version;
-      hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
-    };
-    patches = (old.patches or [ ]) ++ [
-      # Fixes e.g. onnxruntime on aarch64-darwin:
-      # https://hydra.nixos.org/build/248915128/nixlog/1,
-      # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
-      #
-      # The patch is from
-      # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
-      # which is two years old,
-      # but Eigen hasn't had a release in two years either:
-      # https://gitlab.com/libeigen/eigen/-/issues/2699.
-      (fetchpatch {
-        url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
-        hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
-      })
-    ];
-  });
-in
-
 stdenv.mkDerivation (finalAttrs: {
   pname = "kstars";
   version = "3.7.5";
@@ -70,7 +39,7 @@ stdenv.mkDerivation (finalAttrs: {
     breeze-icons
     cfitsio
     curl
-    eigen'
+    eigen_3_4_0
     gsl
     indi-full
     kconfig
diff --git a/pkgs/development/libraries/eigen/3.4.0.nix b/pkgs/development/libraries/eigen/3.4.0.nix
new file mode 100644
index 000000000000..069f486cb285
--- /dev/null
+++ b/pkgs/development/libraries/eigen/3.4.0.nix
@@ -0,0 +1,49 @@
+{
+  lib,
+  stdenv,
+  fetchFromGitLab,
+  fetchpatch,
+  cmake,
+}:
+
+stdenv.mkDerivation rec {
+  pname = "eigen";
+  version = "3.4.0";
+
+  src = fetchFromGitLab {
+    owner = "libeigen";
+    repo = "eigen";
+    rev = version;
+    hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
+  };
+
+  patches = [
+    ./include-dir.patch
+    # Fixes e.g. onnxruntime on aarch64-darwin:
+    # https://hydra.nixos.org/build/248915128/nixlog/1,
+    # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
+    #
+    # The patch is from
+    # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
+    # which is two years old,
+    # but Eigen hasn't had a release in two years either:
+    # https://gitlab.com/libeigen/eigen/-/issues/2699.
+    (fetchpatch {
+      url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
+      hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
+    })
+  ];
+
+  nativeBuildInputs = [ cmake ];
+
+  meta = with lib; {
+    homepage = "https://eigen.tuxfamily.org";
+    description = "C++ template library for linear algebra: vectors, matrices, and related algorithms";
+    license = licenses.lgpl3Plus;
+    maintainers = with maintainers; [
+      sander
+      raskin
+    ];
+    platforms = platforms.unix;
+  };
+}
diff --git a/pkgs/development/libraries/libfive/default.nix b/pkgs/development/libraries/libfive/default.nix
index dbb9fc8109ce..141bd8f17b2c 100644
--- a/pkgs/development/libraries/libfive/default.nix
+++ b/pkgs/development/libraries/libfive/default.nix
@@ -3,13 +3,11 @@
   stdenv,
   wrapQtAppsHook,
   fetchFromGitHub,
-  fetchFromGitLab,
-  fetchpatch,
   unstableGitUpdater,
   cmake,
   ninja,
   pkg-config,
-  eigen,
+  eigen_3_4_0,
   zlib,
   libpng,
   boost,
@@ -38,32 +36,7 @@ stdenv.mkDerivation {
     python.pkgs.pythonImportsCheckHook
   ];
   buildInputs = [
-    # reverts 'eigen: 3.4.0 -> 3.4.0-unstable-2022-05-19'
-    # https://github.com/nixos/nixpkgs/commit/d298f046edabc84b56bd788e11eaf7ed72f8171c
-    (eigen.overrideAttrs (old: rec {
-      version = "3.4.0";
-      src = fetchFromGitLab {
-        owner = "libeigen";
-        repo = "eigen";
-        rev = version;
-        hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
-      };
-      patches = (old.patches or [ ]) ++ [
-        # Fixes e.g. onnxruntime on aarch64-darwin:
-        # https://hydra.nixos.org/build/248915128/nixlog/1,
-        # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
-        #
-        # The patch is from
-        # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
-        # which is two years old,
-        # but Eigen hasn't had a release in two years either:
-        # https://gitlab.com/libeigen/eigen/-/issues/2699.
-        (fetchpatch {
-          url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
-          hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
-        })
-      ];
-    }))
+    eigen_3_4_0
     zlib
     libpng
     boost
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 83f48cfe8b1f..2f5c84ae72e6 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -9178,6 +9178,8 @@ with pkgs;
 
   eigen = callPackage ../development/libraries/eigen { };
 
+  eigen_3_4_0 = callPackage ../development/libraries/eigen/3.4.0.nix { };
+
   eigen2 = callPackage ../development/libraries/eigen/2.0.nix { };
 
   vapoursynth-editor = libsForQt5.callPackage ../by-name/va/vapoursynth/editor.nix { };