From fef053dbdaf6e07c4da07883895df7439fab36dc Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 17:40:20 +0200
Subject: [PATCH 01/10] openmpCheckPhaseHook: init

(cherry picked from commit 8ff970916b975cfd1b79ff3751061526fe88614b)
---
 .../op/openmpCheckPhaseHook/omp-check-hook.sh        | 11 +++++++++++
 pkgs/by-name/op/openmpCheckPhaseHook/package.nix     | 12 ++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 pkgs/by-name/op/openmpCheckPhaseHook/omp-check-hook.sh
 create mode 100644 pkgs/by-name/op/openmpCheckPhaseHook/package.nix

diff --git a/pkgs/by-name/op/openmpCheckPhaseHook/omp-check-hook.sh b/pkgs/by-name/op/openmpCheckPhaseHook/omp-check-hook.sh
new file mode 100644
index 000000000000..b3279b170360
--- /dev/null
+++ b/pkgs/by-name/op/openmpCheckPhaseHook/omp-check-hook.sh
@@ -0,0 +1,11 @@
+preCheckHooks+=('setupOmpCheck')
+preInstallCheckHooks+=('setupOmpCheck')
+
+
+setupOmpCheck() {
+  # Limit number of OpenMP threads. Default is "all cores".
+  # Using all cores causes high load on builders if checks are executed with NIX_BUILD_CORE parallelism.
+  # This gets even worse if multiple builds are scheduled on the same machine, potentially growing O(n^3) without explicit core limits.
+  export OMP_NUM_THREADS="${OMP_NUM_THREADS:-1}"
+}
+
diff --git a/pkgs/by-name/op/openmpCheckPhaseHook/package.nix b/pkgs/by-name/op/openmpCheckPhaseHook/package.nix
new file mode 100644
index 000000000000..9e30609e8de5
--- /dev/null
+++ b/pkgs/by-name/op/openmpCheckPhaseHook/package.nix
@@ -0,0 +1,12 @@
+{
+  lib,
+  makeSetupHook,
+}:
+
+makeSetupHook {
+  name = "omp-checkPhase-hook";
+
+  __structuredAttrs = true;
+
+  meta.license = lib.licenses.mit;
+} ./omp-check-hook.sh

From c603d87dad3987d9e833d001fa813789ddca0c63 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 17:50:01 +0200
Subject: [PATCH 02/10] doc/openmpCheckPhaseHook: init

(cherry picked from commit 71fbdd6512fcf27434aa34bbb9a830c1a8a2068b)
---
 doc/hooks/index.md                     |  1 +
 doc/hooks/openmp-check-hook.section.md | 10 ++++++++++
 doc/redirects.json                     |  3 +++
 3 files changed, 14 insertions(+)
 create mode 100644 doc/hooks/openmp-check-hook.section.md

diff --git a/doc/hooks/index.md b/doc/hooks/index.md
index bac8306ff10e..e6c3af542f07 100644
--- a/doc/hooks/index.md
+++ b/doc/hooks/index.md
@@ -34,6 +34,7 @@ nodejs-install-manuals.section.md
 npm-build-hook.section.md
 npm-config-hook.section.md
 npm-install-hook.section.md
+openmp-check-hook.section.md
 patch-rc-path-hooks.section.md
 perl.section.md
 pkg-config.section.md
diff --git a/doc/hooks/openmp-check-hook.section.md b/doc/hooks/openmp-check-hook.section.md
new file mode 100644
index 000000000000..5a5842eb5e29
--- /dev/null
+++ b/doc/hooks/openmp-check-hook.section.md
@@ -0,0 +1,10 @@
+# openmpCheckPhaseHook {#setup-hook-omp-check}
+
+
+This hook can be used to setup a check phase that
+requires running a OpenMP application. It mostly
+serves to limit `OMP_NUM_THREADS` to avoid overloading
+build machines.
+
+This hook will not attempt to override an already existing
+definition of `OMP_NUM_THREADS` in the environment.
diff --git a/doc/redirects.json b/doc/redirects.json
index de13226671e4..8a822e998401 100644
--- a/doc/redirects.json
+++ b/doc/redirects.json
@@ -2809,6 +2809,9 @@
   "setup-hook-mpi-check": [
     "index.html#setup-hook-mpi-check"
   ],
+  "setup-hook-omp-check": [
+    "index.html#setup-hook-omp-check"
+  ],
   "ninja": [
     "index.html#ninja"
   ],

From dd5eb4395bff0f12925052887361f8724d0055ca Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 17:51:33 +0200
Subject: [PATCH 03/10] mpiCheckPhaseHook: propagate openmpCheckPhaseHook

(cherry picked from commit 240ef095c6bc783e437fb69b74442db6219d0e49)
---
 pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh | 3 ---
 pkgs/by-name/mp/mpiCheckPhaseHook/package.nix       | 6 +++++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh b/pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh
index be2203951c0f..139dc932366f 100644
--- a/pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh
+++ b/pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh
@@ -72,8 +72,5 @@ setupMpiCheck() {
       export HWLOC_XMLFILE="@topology@"
       ;;
   esac
-
-  # Limit number of OpenMP threads. Default is "all cores".
-  export OMP_NUM_THREADS=1
 }
 
diff --git a/pkgs/by-name/mp/mpiCheckPhaseHook/package.nix b/pkgs/by-name/mp/mpiCheckPhaseHook/package.nix
index c771e87376fa..c380087e77bf 100644
--- a/pkgs/by-name/mp/mpiCheckPhaseHook/package.nix
+++ b/pkgs/by-name/mp/mpiCheckPhaseHook/package.nix
@@ -1,7 +1,7 @@
 {
-  callPackage,
   makeSetupHook,
   stdenv,
+  openmpCheckPhaseHook,
 }:
 
 makeSetupHook {
@@ -11,4 +11,8 @@ makeSetupHook {
     iface = if stdenv.hostPlatform.isDarwin then "lo0" else "lo";
     topology = ./topology.xml;
   };
+
+  propagatedNativeBuildInputs = [
+    openmpCheckPhaseHook
+  ];
 } ./mpi-check-hook.sh

From ae16e5685384e05af406b047968dce2ad3445c95 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 17:52:29 +0200
Subject: [PATCH 04/10] llvmPackages.openmp: propagate openmpCheckPhaseHook

(cherry picked from commit 559ae88af990e9cc835f791f1fca62283ac574a7)
---
 pkgs/development/compilers/llvm/common/openmp/default.nix | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkgs/development/compilers/llvm/common/openmp/default.nix b/pkgs/development/compilers/llvm/common/openmp/default.nix
index a08376522d9e..10f9ce154cb4 100644
--- a/pkgs/development/compilers/llvm/common/openmp/default.nix
+++ b/pkgs/development/compilers/llvm/common/openmp/default.nix
@@ -19,7 +19,7 @@
   ompdSupport ? true,
   ompdGdbSupport ? ompdSupport,
   getVersionFile,
-  fetchpatch,
+  openmpCheckPhaseHook,
 }:
 
 assert lib.assertMsg (ompdGdbSupport -> ompdSupport) "OMPD GDB support requires OMPD support!";
@@ -60,6 +60,10 @@ stdenv.mkDerivation (finalAttrs: {
     lit
   ];
 
+  propagatedNativeBuildInputs = [
+    openmpCheckPhaseHook
+  ];
+
   buildInputs = [
     llvm
   ]

From 04a27bf02fa6f1bb2ab153e7e0af18a9ca79bbb0 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 17:53:36 +0200
Subject: [PATCH 05/10] blas: propagate openmpCheckPhaseHook

(cherry picked from commit df838c503eaeb72f9a100ccf8e5914fe65a11502)
---
 pkgs/by-name/bl/blas/package.nix | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pkgs/by-name/bl/blas/package.nix b/pkgs/by-name/bl/blas/package.nix
index 01ad1839c339..51deec6c5c64 100644
--- a/pkgs/by-name/bl/blas/package.nix
+++ b/pkgs/by-name/bl/blas/package.nix
@@ -3,6 +3,7 @@
   stdenv,
   lapack-reference,
   openblas,
+  openmpCheckPhaseHook,
   isILP64 ? false,
   blasProvider ? openblas,
 }:
@@ -186,6 +187,10 @@ stdenv.mkDerivation {
     "dev"
   ];
 
+  propagatedNativeBuildInputs = [
+    openmpCheckPhaseHook
+  ];
+
   meta = (blasProvider'.meta or { }) // {
     description = "${lib.getName blasProvider} with just the BLAS C and FORTRAN ABI";
   };

From ace3e0ed624ded2153086d55b6e84df13dc5e5c9 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 18:42:53 +0200
Subject: [PATCH 06/10] python3Packages.numpy: propagate openmpCheckPhaseHook

(cherry picked from commit b3944a1e306623cb152573d1aaad9ba569a9d67f)
---
 pkgs/development/python-modules/numpy/2.nix | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pkgs/development/python-modules/numpy/2.nix b/pkgs/development/python-modules/numpy/2.nix
index 67c60475fd5f..22d2b00dcd9b 100644
--- a/pkgs/development/python-modules/numpy/2.nix
+++ b/pkgs/development/python-modules/numpy/2.nix
@@ -19,6 +19,8 @@
   coreutils,
   lapack,
 
+  openmpCheckPhaseHook,
+
   # Reverse dependency
   sage,
 
@@ -113,6 +115,10 @@ buildPythonPackage (finalAttrs: {
     typing-extensions
   ];
 
+  propagatedNativeBuildInputs = [
+    openmpCheckPhaseHook
+  ];
+
   preCheck = ''
     pushd $out
     # For numpy-config executable to be available during tests

From 39200d69a6ce7291380446e78f403fdc88b1e7a0 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 18:43:24 +0200
Subject: [PATCH 07/10] python3Packages.*: remove explicit OMP_NUM_THREADS
 definitions where numpy is used

(cherry picked from commit ef8b8d8f58919deb3d462416e582dadafe3fb833)
---
 pkgs/development/python-modules/astropy/default.nix      | 4 ----
 pkgs/development/python-modules/geometric/default.nix    | 4 ----
 pkgs/development/python-modules/imread/default.nix       | 1 -
 pkgs/development/python-modules/numpy/1.nix              | 7 ++++++-
 pkgs/development/python-modules/numpy/2.nix              | 4 ----
 pkgs/development/python-modules/pyscf/default.nix        | 1 -
 pkgs/development/python-modules/qutip/default.nix        | 1 -
 pkgs/development/python-modules/scikit-learn/default.nix | 1 -
 pkgs/development/python-modules/scipy/default.nix        | 5 -----
 9 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/pkgs/development/python-modules/astropy/default.nix b/pkgs/development/python-modules/astropy/default.nix
index 639e234acbb0..94376d603d5e 100644
--- a/pkgs/development/python-modules/astropy/default.nix
+++ b/pkgs/development/python-modules/astropy/default.nix
@@ -143,10 +143,6 @@ buildPythonPackage rec {
 
   preCheck = ''
     export HOME="$(mktemp -d)"
-    export OMP_NUM_THREADS=$(( $NIX_BUILD_CORES / 4 ))
-    if [ $OMP_NUM_THREADS -eq 0 ]; then
-      export OMP_NUM_THREADS=1
-    fi
 
     # See https://github.com/astropy/astropy/issues/17649 and see
     # --hypothesis-profile=ci pytest flag below.
diff --git a/pkgs/development/python-modules/geometric/default.nix b/pkgs/development/python-modules/geometric/default.nix
index ec1553e164ab..08301b669d5c 100644
--- a/pkgs/development/python-modules/geometric/default.nix
+++ b/pkgs/development/python-modules/geometric/default.nix
@@ -28,10 +28,6 @@ buildPythonPackage rec {
     six
   ];
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   nativeCheckInputs = [ pytestCheckHook ];
 
   meta = {
diff --git a/pkgs/development/python-modules/imread/default.nix b/pkgs/development/python-modules/imread/default.nix
index a26b89fb2b02..bc0934f5bd7c 100644
--- a/pkgs/development/python-modules/imread/default.nix
+++ b/pkgs/development/python-modules/imread/default.nix
@@ -49,7 +49,6 @@ buildPythonPackage rec {
   preCheck = ''
     cd $TMPDIR
     export HOME=$TMPDIR
-    export OMP_NUM_THREADS=1
   '';
 
   meta = {
diff --git a/pkgs/development/python-modules/numpy/1.nix b/pkgs/development/python-modules/numpy/1.nix
index 4fc274257916..7167ff94637e 100644
--- a/pkgs/development/python-modules/numpy/1.nix
+++ b/pkgs/development/python-modules/numpy/1.nix
@@ -18,6 +18,8 @@
   blas,
   lapack,
 
+  openmpCheckPhaseHook,
+
   # Reverse dependency
   sage,
 
@@ -93,7 +95,6 @@ buildPythonPackage (finalAttrs: {
   # see https://github.com/OpenMathLib/OpenBLAS/issues/2993
   preConfigure = ''
     sed -i 's/-faltivec//' numpy/distutils/system_info.py
-    export OMP_NUM_THREADS=$((NIX_BUILD_CORES > 64 ? 64 : NIX_BUILD_CORES))
   '';
 
   preBuild = ''
@@ -110,6 +111,10 @@ buildPythonPackage (finalAttrs: {
     typing-extensions
   ];
 
+  propagatedNativeBuildInputs = [
+    openmpCheckPhaseHook
+  ];
+
   preCheck = ''
     cd "$out"
   '';
diff --git a/pkgs/development/python-modules/numpy/2.nix b/pkgs/development/python-modules/numpy/2.nix
index 22d2b00dcd9b..0cef4e21ccc0 100644
--- a/pkgs/development/python-modules/numpy/2.nix
+++ b/pkgs/development/python-modules/numpy/2.nix
@@ -88,12 +88,8 @@ buildPythonPackage (finalAttrs: {
   ]
   ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [ mesonEmulatorHook ];
 
-  # we default openblas to build with 64 threads
-  # if a machine has more than 64 threads, it will segfault
-  # see https://github.com/OpenMathLib/OpenBLAS/issues/2993
   preConfigure = ''
     sed -i 's/-faltivec//' numpy/distutils/system_info.py
-    export OMP_NUM_THREADS=$((NIX_BUILD_CORES > 64 ? 64 : NIX_BUILD_CORES))
   '';
 
   buildInputs = [
diff --git a/pkgs/development/python-modules/pyscf/default.nix b/pkgs/development/python-modules/pyscf/default.nix
index 9028317762b5..8444a005e775 100644
--- a/pkgs/development/python-modules/pyscf/default.nix
+++ b/pkgs/development/python-modules/pyscf/default.nix
@@ -61,7 +61,6 @@ buildPythonPackage {
   preCheck = ''
     # Set config used by tests to ensure reproducibility
     echo 'pbc_tools_pbc_fft_engine = "NUMPY"' > pyscf/pyscf_config.py
-    export OMP_NUM_THREADS=1
     ulimit -s 20000
     export PYSCF_CONFIG_FILE=$(pwd)/pyscf/pyscf_config.py
   '';
diff --git a/pkgs/development/python-modules/qutip/default.nix b/pkgs/development/python-modules/qutip/default.nix
index 89e77b995785..aa968f51180d 100644
--- a/pkgs/development/python-modules/qutip/default.nix
+++ b/pkgs/development/python-modules/qutip/default.nix
@@ -62,7 +62,6 @@ buildPythonPackage (finalAttrs: {
   # This is due to the Cython-compiled modules not being in the correct location
   # of the source tree.
   preCheck = ''
-    export OMP_NUM_THREADS=$NIX_BUILD_CORES
     mkdir -p test && cd test
   '';
 
diff --git a/pkgs/development/python-modules/scikit-learn/default.nix b/pkgs/development/python-modules/scikit-learn/default.nix
index b48f5a5d8f72..bf50ab0b7a63 100644
--- a/pkgs/development/python-modules/scikit-learn/default.nix
+++ b/pkgs/development/python-modules/scikit-learn/default.nix
@@ -116,7 +116,6 @@ buildPythonPackage rec {
   preCheck = ''
     cd $TMPDIR
     export HOME=$TMPDIR
-    export OMP_NUM_THREADS=1
   '';
 
   pythonImportsCheck = [ "sklearn" ];
diff --git a/pkgs/development/python-modules/scipy/default.nix b/pkgs/development/python-modules/scipy/default.nix
index cdecd986e4ef..30999320f1e8 100644
--- a/pkgs/development/python-modules/scipy/default.nix
+++ b/pkgs/development/python-modules/scipy/default.nix
@@ -190,11 +190,6 @@ buildPythonPackage (finalAttrs: {
   '';
 
   preCheck = ''
-    export OMP_NUM_THREADS=$(( $NIX_BUILD_CORES / 4 ))
-    if [ $OMP_NUM_THREADS -eq 0 ]; then
-      export OMP_NUM_THREADS=1
-    fi
-
     cd $out
   '';
 

From 19bbab8a7fa668879b91d65467416b861cd8b63e Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 18:16:07 +0200
Subject: [PATCH 08/10] treewide: remove explicit OMP_NUM_THREADS where
 openmpCheckPhaseHook is in effect

(cherry picked from commit d5ae461bf7277e6fcbb5239e4b268ed2792e6ef2)
---
 pkgs/by-name/df/dftd4/package.nix                            | 4 ----
 pkgs/by-name/el/elpa/package.nix                             | 3 ---
 pkgs/by-name/er/ergoscf/package.nix                          | 1 -
 pkgs/by-name/gr/greenx/package.nix                           | 4 ----
 pkgs/by-name/mc/mctc-lib/package.nix                         | 4 ----
 pkgs/by-name/mo/mopac/package.nix                            | 4 ----
 pkgs/by-name/mp/mpb/package.nix                              | 2 --
 pkgs/by-name/mu/multicharge/package.nix                      | 4 ----
 pkgs/by-name/pi/pixman/package.nix                           | 5 -----
 pkgs/by-name/wa/wannier90/package.nix                        | 3 ---
 .../libraries/science/chemistry/simple-dftd3/default.nix     | 3 ---
 .../libraries/science/chemistry/tblite/default.nix           | 4 ----
 12 files changed, 41 deletions(-)

diff --git a/pkgs/by-name/df/dftd4/package.nix b/pkgs/by-name/df/dftd4/package.nix
index 47bdd3495224..3167f58ca71f 100644
--- a/pkgs/by-name/df/dftd4/package.nix
+++ b/pkgs/by-name/df/dftd4/package.nix
@@ -82,10 +82,6 @@ stdenv.mkDerivation (finalAttrs: {
       app/tester.py
   '';
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   meta = {
     description = "Generally Applicable Atomic-Charge Dependent London Dispersion Correction";
     mainProgram = "dftd4";
diff --git a/pkgs/by-name/el/elpa/package.nix b/pkgs/by-name/el/elpa/package.nix
index 170f03f697e8..650d59f93de4 100644
--- a/pkgs/by-name/el/elpa/package.nix
+++ b/pkgs/by-name/el/elpa/package.nix
@@ -116,9 +116,6 @@ stdenv.mkDerivation (finalAttrs: {
   preCheck = ''
     #patchShebangs ./
 
-    # Run dual threaded
-    export OMP_NUM_THREADS=2
-
     # Reduce test problem sizes
     export TEST_FLAGS="1500 50 16"
   '';
diff --git a/pkgs/by-name/er/ergoscf/package.nix b/pkgs/by-name/er/ergoscf/package.nix
index 9514bb89f1e4..59ccb179b2bd 100644
--- a/pkgs/by-name/er/ergoscf/package.nix
+++ b/pkgs/by-name/er/ergoscf/package.nix
@@ -39,7 +39,6 @@ stdenv.mkDerivation (finalAttrs: {
       "-lblas"
       "-llapack"
     ];
-    OMP_NUM_THREADS = 2; # required for check phase
   };
 
   enableParallelBuilding = true;
diff --git a/pkgs/by-name/gr/greenx/package.nix b/pkgs/by-name/gr/greenx/package.nix
index c08356a17058..fb360c6728b8 100644
--- a/pkgs/by-name/gr/greenx/package.nix
+++ b/pkgs/by-name/gr/greenx/package.nix
@@ -34,10 +34,6 @@ stdenv.mkDerivation (finalAttrs: {
   # Uses a hacky python setup run by cmake, which is hard to get running
   doCheck = false;
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   meta = {
     description = "Library for Green’s function based electronic structure theory calculations";
     license = [ lib.licenses.asl20 ];
diff --git a/pkgs/by-name/mc/mctc-lib/package.nix b/pkgs/by-name/mc/mctc-lib/package.nix
index 3473b3dbaa7e..2a11a84f94db 100644
--- a/pkgs/by-name/mc/mctc-lib/package.nix
+++ b/pkgs/by-name/mc/mctc-lib/package.nix
@@ -61,10 +61,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   doCheck = true;
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   postPatch = ''
     patchShebangs --build config/install-mod.py
   '';
diff --git a/pkgs/by-name/mo/mopac/package.nix b/pkgs/by-name/mo/mopac/package.nix
index c5e5dacccb9b..c70b46ded59c 100644
--- a/pkgs/by-name/mo/mopac/package.nix
+++ b/pkgs/by-name/mo/mopac/package.nix
@@ -39,10 +39,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   doCheck = true;
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   meta = {
     description = "Semiempirical quantum chemistry";
     homepage = "https://github.com/openmopac/mopac";
diff --git a/pkgs/by-name/mp/mpb/package.nix b/pkgs/by-name/mp/mpb/package.nix
index eb001a94446d..f92f7bfeeadf 100644
--- a/pkgs/by-name/mp/mpb/package.nix
+++ b/pkgs/by-name/mp/mpb/package.nix
@@ -59,8 +59,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   doCheck = true;
 
-  preCheck = "export OMP_NUM_THREADS=2";
-
   meta = {
     description = "MIT Photonic-Bands: computation of photonic band structures in periodic media";
     homepage = "https://mpb.readthedocs.io/en/latest/";
diff --git a/pkgs/by-name/mu/multicharge/package.nix b/pkgs/by-name/mu/multicharge/package.nix
index b4fcbe0cf512..a6192b7993db 100644
--- a/pkgs/by-name/mu/multicharge/package.nix
+++ b/pkgs/by-name/mu/multicharge/package.nix
@@ -71,10 +71,6 @@ stdenv.mkDerivation (finalAttrs: {
     patchShebangs --build config/install-mod.py
   '';
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   meta = {
     description = "Electronegativity equilibration model for atomic partial charges";
     mainProgram = "multicharge";
diff --git a/pkgs/by-name/pi/pixman/package.nix b/pkgs/by-name/pi/pixman/package.nix
index 367fa018c860..3ef554a9eb07 100644
--- a/pkgs/by-name/pi/pixman/package.nix
+++ b/pkgs/by-name/pi/pixman/package.nix
@@ -61,11 +61,6 @@ stdenv.mkDerivation (finalAttrs: {
     "-Dneon=disabled"
   ];
 
-  preConfigure = ''
-    # https://gitlab.freedesktop.org/pixman/pixman/-/issues/62
-    export OMP_NUM_THREADS=$((NIX_BUILD_CORES > 184 ? 184 : NIX_BUILD_CORES))
-  '';
-
   enableParallelBuilding = true;
 
   doCheck = !stdenv.hostPlatform.isDarwin;
diff --git a/pkgs/by-name/wa/wannier90/package.nix b/pkgs/by-name/wa/wannier90/package.nix
index 2a8996daf779..321c34e4e0e7 100644
--- a/pkgs/by-name/wa/wannier90/package.nix
+++ b/pkgs/by-name/wa/wannier90/package.nix
@@ -73,9 +73,6 @@ stdenv.mkDerivation (finalAttrs: {
   doCheck = true;
   checkInputs = [ python3 ];
   checkTarget = [ "test-serial" ];
-  preCheck = ''
-    export OMP_NUM_THREADS=4
-  '';
 
   enableParallelBuilding = true;
 
diff --git a/pkgs/development/libraries/science/chemistry/simple-dftd3/default.nix b/pkgs/development/libraries/science/chemistry/simple-dftd3/default.nix
index 1310bf160d8b..ce76e5c599d3 100644
--- a/pkgs/development/libraries/science/chemistry/simple-dftd3/default.nix
+++ b/pkgs/development/libraries/science/chemistry/simple-dftd3/default.nix
@@ -64,9 +64,6 @@ stdenv.mkDerivation rec {
   ];
 
   doCheck = true;
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
 
   meta = {
     description = "Reimplementation of the DFT-D3 program";
diff --git a/pkgs/development/libraries/science/chemistry/tblite/default.nix b/pkgs/development/libraries/science/chemistry/tblite/default.nix
index bd40a12cea03..db3734562e15 100644
--- a/pkgs/development/libraries/science/chemistry/tblite/default.nix
+++ b/pkgs/development/libraries/science/chemistry/tblite/default.nix
@@ -88,10 +88,6 @@ stdenv.mkDerivation rec {
 
   doCheck = buildType == "meson";
 
-  preCheck = ''
-    export OMP_NUM_THREADS=2
-  '';
-
   meta = {
     description = "Light-weight tight-binding framework";
     mainProgram = "tblite";

From 5646fd9ed14b1118bcb8a4c523419f0278ef2a41 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 18:16:24 +0200
Subject: [PATCH 09/10] pixman: use openmpCheckPhaseHook

(cherry picked from commit cd137f1c889116425f507d709e709dead46dbcea)
---
 pkgs/by-name/pi/pixman/package.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pkgs/by-name/pi/pixman/package.nix b/pkgs/by-name/pi/pixman/package.nix
index 3ef554a9eb07..23755586fe6c 100644
--- a/pkgs/by-name/pi/pixman/package.nix
+++ b/pkgs/by-name/pi/pixman/package.nix
@@ -6,6 +6,7 @@
   ninja,
   pkg-config,
   libpng,
+  openmpCheckPhaseHook,
   glib, # just passthru
 
   # for passthru.tests
@@ -46,6 +47,7 @@ stdenv.mkDerivation (finalAttrs: {
     meson
     ninja
     pkg-config
+    openmpCheckPhaseHook
     __flattenIncludeHackHook
   ];
 

From ca1b547ed93deac31f563d05170bf7db95f2de81 Mon Sep 17 00:00:00 2001
From: Grimmauld <Grimmauld@grimmauld.de>
Date: Fri, 26 Jun 2026 18:16:50 +0200
Subject: [PATCH 10/10] mctc-lib: use openmpCheckPhaseHook

(cherry picked from commit 576031cf3c432361b33dff42e71ce639518a9219)
---
 pkgs/by-name/mc/mctc-lib/package.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pkgs/by-name/mc/mctc-lib/package.nix b/pkgs/by-name/mc/mctc-lib/package.nix
index 2a11a84f94db..ed313b3bc7ca 100644
--- a/pkgs/by-name/mc/mctc-lib/package.nix
+++ b/pkgs/by-name/mc/mctc-lib/package.nix
@@ -10,6 +10,7 @@
   pkg-config,
   python3,
   jonquil,
+  openmpCheckPhaseHook,
 }:
 
 assert (
@@ -43,6 +44,7 @@ stdenv.mkDerivation (finalAttrs: {
     gfortran
     pkg-config
     python3
+    openmpCheckPhaseHook
   ]
   ++ lib.optionals (buildType == "meson") [
     meson