diff --git a/python/setup.py b/python/setup.py
index 7580b7d..e32c2ca 100644
--- a/python/setup.py
+++ b/python/setup.py
@@ -51,6 +51,7 @@ setup(
   package_data={'openEMS': ['*.pxd']},
   python_requires='>=3.9',
   install_requires=[
+    'cython>=3.0.6',  # Apache License 2.0 (https://github.com/cython/cython/blob/master/LICENSE.txt)
     'h5py>=3.10.0',   # BSD 3-Clause (https://github.com/h5py/h5py/blob/master/LICENSE)
     'numpy>=1.26.2',  # BSD 3-Clause (https://github.com/numpy/numpy/blob/main/LICENSE.txt)
   ],