diff --git a/pyproject.toml b/pyproject.toml
index c336af4da..29eb691d8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -59,6 +59,9 @@ zip-safe = true
 [tool.setuptools.packages.find]
 where = ['src']
 
+[tool.setuptools.package-data]
+'stcal.ramp_fitting.src' = ['*.c']
+
 [tool.pytest.ini_options]
 minversion = 4.6
 doctest_plus = true
diff --git a/setup.py b/setup.py
index 5265a7231..9a2ebbd9d 100644
--- a/setup.py
+++ b/setup.py
@@ -1,38 +1,32 @@
 from setuptools import setup, find_packages, Extension
-# from Cython.Build import cythonize
-# from Cython.Compiler import Options
+from Cython.Build import cythonize
+from Cython.Compiler import Options
 import numpy as np
 
-'''
 Options.docstrings = True
 Options.annotate = False
 
-extensions = [Extension('stcal.ramp_fitting.ols_cas22',
-                        ['src/stcal/ramp_fitting/ols_cas22.pyx'],
-                        include_dirs=[np.get_include()],
-                        extra_compile_args=['-std=c99'])]
-                        include_dirs=[np.get_include()])]
-'''
-
-# package_data values are glob patterns relative to each specific subpackage.
-package_data = {
-    "stcal.ramp_fitting.src": ["*.c"],
-}
-
 # Setup C module include directories
 include_dirs = [np.get_include()]
 
 # Setup C module macros
 define_macros = [("NUMPY", "1")]
 
+extensions = [
+    Extension(
+        'stcal.ramp_fitting.ols_cas22',
+        ['src/stcal/ramp_fitting/ols_cas22.pyx'],
+        include_dirs=include_dirs,
+        extra_compile_args=['-std=c99']
+    ),
+    Extension(
+        "stcal.ramp_fitting.slope_fitter",
+        ["src/stcal/ramp_fitting/src/slope_fitter.c"],
+        include_dirs=include_dirs,
+        define_macros=define_macros,
+    ),
+]
+
 setup(
-    ext_modules=[
-        Extension(
-            "stcal.ramp_fitting.slope_fitter",
-            ["src/stcal/ramp_fitting/src/slope_fitter.c"],
-            include_dirs=include_dirs,
-            define_macros=define_macros,
-        ),
-        # cythonize(extensions),
-    ],
+    ext_modules=cythonize(extensions),
 )