diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 1f3a76726a..b384d594ab 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -39,6 +39,7 @@ jobs:
           - ubuntu-latest
           - macos-13
         python-version:
+          - '3.13t'
           - '3.13'
           - '3.12'
           - '3.11'
@@ -81,7 +82,7 @@ jobs:
           submodules: true
 
       - name: 'Python ${{ matrix.python-version }}'
-        uses: actions/setup-python@v5
+        uses: Quansight-Labs/setup-python@v5
         with:
           python-version: '${{ matrix.python-version }}'
           architecture: '${{ matrix.python-architecture }}'
diff --git a/awkward-cpp/src/python/_ext.cpp b/awkward-cpp/src/python/_ext.cpp
index 846bd33f54..e7900462be 100644
--- a/awkward-cpp/src/python/_ext.cpp
+++ b/awkward-cpp/src/python/_ext.cpp
@@ -9,7 +9,7 @@
 #include "awkward/python/forth.h"
 
 namespace py = pybind11;
-PYBIND11_MODULE(_ext, m) {
+PYBIND11_MODULE(_ext, m, py::mod_gil_not_used()) {
 #ifdef VERSION_INFO
   m.attr("__version__") = VERSION_INFO;
 #else