diff --git a/README.rst b/README.rst
index db1ebbf..8680298 100644
--- a/README.rst
+++ b/README.rst
@@ -52,9 +52,11 @@ of the project::
 Testing
 =======
 
-The regression testsuite utilizes the `pytest` framework and may be executed by
+The regression testsuite utilizes the `pytest` framework and may be installed
+and executed by
 ::
 
+  pip install .[test]
   python -m pytest --basetemp=Testing
 
 Documentation
diff --git a/pyproject.toml b/pyproject.toml
index 5ce2510..a1a38d5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,30 @@
-[build-system]
-requires = ['setuptools', 'wheel', 'pytest', 'numpy', 'h5py', 'ase']
-build-backend = 'setuptools.build_meta'
\ No newline at end of file
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[project]
+name = "fortnet-python"
+version = "0.4"
+authors = [{name = "T. W. van der Heide"},]
+dependencies = ["numpy", "h5py", "ase"]
+requires-python = ">=3.10"
+description = "Python Tools for the Fortnet Software Package"
+readme = {file = "README.rst", content-type = "text/x-rst"}
+license = {text = "BSD"}
+classifiers = [
+  "Development Status :: 5 - Production/Stable",
+  "Intended Audience :: Science/Research",
+  "License :: OSI Approved :: BSD License",
+  "Programming Language :: Python :: 3",
+  "Environment :: Console",
+  "Operating System :: OS Independent",
+  "Topic :: Scientific/Engineering",
+]
+
+[project.urls]
+Homepage = "https://github.com/vanderhe/fortnet-python"
+Documentation = "https://fortnet.readthedocs.io/en/latest/fortformat/index.html"
+Repository = "https://github.com/vanderhe/fortnet-python.git"
+Issues = "https://github.com/vanderhe/fortnet-python/issues"
+
+[project.optional-dependencies]
+test = ["pytest",]
diff --git a/setup.cfg b/setup.cfg
deleted file mode 100644
index 1ee629c..0000000
--- a/setup.cfg
+++ /dev/null
@@ -1,35 +0,0 @@
-[metadata]
-name = fortnet-python
-version = 0.4
-author = T. W. van der Heide
-author_email = vanderhe@uni-bremen.de
-url = https://github.com/vanderhe/fortnet-python
-description = Python Tools for the Fortnet Software Package
-long_description = file: README.rst
-long_description_content_type = text/x-rst
-license = BSD
-license_file = LICENSE
-platform = any
-classifiers =
-    Intended Audience :: Developers
-    License :: OSI Approved :: BSD License
-    Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.7
-    Programming Language :: Python :: 3.8
-    Programming Language :: Python :: 3.9
-
-[options]
-include_package_data = True
-package_dir =
-    = src
-packages = fortformat
-install_requires =
-    wheel
-    setuptools
-    pytest
-    numpy
-    h5py
-    ase
-
-[options.packages.find]
-where = src
diff --git a/setup.py b/setup.py
deleted file mode 100644
index 7c3378a..0000000
--- a/setup.py
+++ /dev/null
@@ -1,15 +0,0 @@
-#!/usr/bin/env python3
-
-'''
-Legacy setup.py file that gathers its
-configuration from setup.cfg and pyproject.toml
-'''
-
-try:
-    from setuptools import setup
-except ImportError:
-    from distutils.core import setup
-
-
-if __name__ == '__main__':
-    setup()
diff --git a/src/fortformat/fnetdata.py b/src/fortformat/fnetdata.py
index 066d1c7..cf8921c 100644
--- a/src/fortformat/fnetdata.py
+++ b/src/fortformat/fnetdata.py
@@ -192,7 +192,7 @@ def _process_data(self):
                     pos = np.where(
                         unique_global_zz == data[isys]['atomicnumbers'][iatom])
                     # Fortran indexing starts at 1
-                    data[isys]['localattoglobalsp'][iatom] = pos[0] + 1
+                    data[isys]['localattoglobalsp'][iatom] = pos[0].item() + 1
 
         return data, unique_global_zz