diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index bdd164e67..675b72cd7 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -496,60 +496,59 @@ jobs:
     #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
     # Stage Four - Build / test the SDist  #
     #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
-    # test_sdist:
-    #   needs:
-    #     - initialize
-    #     - build_sdist
-
-    #   strategy:
-    #     matrix:
-    #       os:
-    #         - ubuntu-22.04
-    #       python-version:
-    #         - 3.9
-
-    #   runs-on: ${{ matrix.os }}
-
-    #   # if: ${{ needs.initialize.outputs.FULL_RUN == 'true' }}
-
-    #   steps:
-    #     - name: Checkout
-    #       uses: actions/checkout@v4
-    #       with:
-    #         submodules: recursive
-
-    #     - name: Set up Python ${{ matrix.python-version }}
-    #       uses: ./.github/actions/setup-python
-    #       with:
-    #         version: '${{ matrix.python-version }}'
-
-    #     - name: Set up Caches
-    #       uses: ./.github/actions/setup-caches
-    #       with:
-    #         cibuildwheel: 'cp39'
-
-    #     # Python
-    #     - name: Install python dependencies
-    #       run: make requirements
-
-    #     # Download sdist
-    #     - uses: actions/download-artifact@v4
-    #       with:
-    #         name: csp-sdist
-    #         path: dist/
-
-    #     # Install sdist
-    #     - name: Install sdist
-    #       run: python -m pip install -U dist/csp*.tar.gz --target .
-    #       env:
-    #         CCACHE_DIR: /host/home/runner/work/csp/csp/.ccache
-    #         VCPKG_DEFAULT_BINARY_CACHE: /host/home/runner/vcpkg_cache
-
-    #     # Test sdist
-    #     - name: Run tests against from-scratch sdist build
-    #       run: make test
-
-    ##########################################################################################################################
+    test_sdist:
+      needs:
+        - initialize
+        - build_sdist
+
+      strategy:
+        matrix:
+          os:
+            - ubuntu-22.04
+          python-version:
+            - 3.9
+
+      runs-on: ${{ matrix.os }}
+
+      if: ${{ needs.initialize.outputs.FULL_RUN == 'true' }}
+
+      steps:
+        - name: Checkout
+          uses: actions/checkout@v4
+          with:
+            submodules: recursive
+
+        - name: Set up Python ${{ matrix.python-version }}
+          uses: ./.github/actions/setup-python
+          with:
+            version: '${{ matrix.python-version }}'
+
+        - name: Set up Caches
+          uses: ./.github/actions/setup-caches
+          with:
+            cibuildwheel: 'cp39'
+
+        # Python
+        - name: Install python dependencies
+          run: make requirements
+
+        # Download sdist
+        - uses: actions/download-artifact@v4
+          with:
+            name: csp-sdist
+            path: dist/
+
+        # Install sdist
+        - name: Install sdist
+          run: python -m pip install -U dist/csp*.tar.gz --target .
+          env:
+            CCACHE_DIR: /home/runner/work/csp/csp/.ccache
+            VCPKG_DEFAULT_BINARY_CACHE: /home/runner/vcpkg_cache
+            VCPKG_DOWNLOADS: /home/runner/vcpkg_download_cache
+
+        # Test sdist
+        - name: Run tests against from-scratch sdist build
+          run: make test
 
 
     #################################
diff --git a/pyproject.toml b/pyproject.toml
index f046f0063..22b0a6281 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,7 @@ version = "0.1.0"
 requires-python = ">=3.8"
 
 dependencies = [
+    "backports.zoneinfo; python_version<'3.9'",
     "numpy",
     "pandas",
     "psutil",