diff --git a/pyproject.toml b/pyproject.toml
index d5970617a7..ac67355937 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,2 +1,2 @@
 [build-system]
-requires = ["setuptools", "wheel", "numpy", "cython"]
+requires = ["setuptools", "wheel", "numpy<1.22", "cython"]
diff --git a/tools/ci/gha-install.sh b/tools/ci/gha-install.sh
index 8c4762e3e4..aa40eb90b1 100755
--- a/tools/ci/gha-install.sh
+++ b/tools/ci/gha-install.sh
@@ -1,10 +1,13 @@
 #!/bin/bash
 set -ex
 
-# Upgrade pip, pytest, numpy before doing anything else
+# Upgrade pip, pytest, numpy before doing anything else.
+# TODO: numpy 1.22 results in several failing tests, so we force a lower version
+# for now (similar change made in pyproject.toml). When this is removed, those
+# tests will need to be updated.
 pip install --upgrade pip
 pip install --upgrade pytest
-pip install --upgrade numpy
+pip install --upgrade "numpy<1.22"
 
 # Install NJOY 2016
 ./tools/ci/gha-install-njoy.sh