diff --git a/pyproject.toml b/pyproject.toml
index 7027356..f21b322 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ requires = ["setuptools>=61", "setuptools-scm"]
 
 [project]
 classifiers = ["Programming Language :: Python :: 3"]
-dependencies = ["h5py", "pint", "python-dateutil", "scipy"]
+dependencies = ["h5py", "pint", "python-dateutil", "scipy", "numpy <2"]
 description = "Read HDF5 data conforming to the NXmx application definition of the NeXus format"
 dynamic = ["version"]
 keywords = ["NeXus", "NXmx"]
diff --git a/requirements.txt b/requirements.txt
index 0fd988e..ceee4a7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,8 +8,9 @@ flexparser==0.3.1
     # via pint
 h5py==3.12.1
     # via nxmx (pyproject.toml)
-numpy==2.1.1
+numpy==1.26.4
     # via
+    #   nxmx (pyproject.toml)
     #   h5py
     #   scipy
 pint==0.24.3