diff --git a/.github/workflows/freethreading_tests.yml b/.github/workflows/freethreading_tests.yml
new file mode 100644
index 000000000..58652e801
--- /dev/null
+++ b/.github/workflows/freethreading_tests.yml
@@ -0,0 +1,46 @@
+name: Free Threading Tests
+on: [push, pull_request]
+jobs:
+  freethreading_tests:
+    name: Free Threaded Build ${{ matrix.os.emoji }} ${{ matrix.os.name }} ${{ matrix.python }}
+    runs-on: ${{ matrix.os.runs-on }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - name: Linux
+            matrix: linux
+            emoji: 🐧
+            runs-on: [ubuntu-latest]
+          - name: macOS intel
+            matrix: macos
+            emoji: 🍎
+            runs-on: [macos-13]
+          - name: macOS silicon
+            matrix: macos
+            emoji: 🍎
+            runs-on: [macos-14]
+          - name: Windows
+            matrix: windows
+            emoji: 🪟
+            runs-on: [windows-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install uv and set the python version
+        uses: astral-sh/setup-uv@v5
+        with:
+          version: "0.7.2"
+          python-version: 3.13t
+          enable-cache: false
+      - name: Set up Python
+        run: uv python install
+      - name: Install Dependencies
+        run: |
+          uv pip install unittest-ft
+      - name: Editable build
+        run: |
+          uv pip install -v -e .
+          python -m pip install unittest-ft
+      - name: Run Tests
+        run: |
+          unittest-ft -r -f -s bitarray.test_bitarray
diff --git a/bitarray/_bitarray.c b/bitarray/_bitarray.c
index d917b7cc8..e892f3c3f 100644
--- a/bitarray/_bitarray.c
+++ b/bitarray/_bitarray.c
@@ -965,7 +965,11 @@ extend_dispatch(bitarrayobject *self, PyObject *obj)
 static PyObject *
 bitarray_all(bitarrayobject *self)
 {
-    return PyBool_FromLong(find_bit(self, 0, 0, self->nbits, 0) == -1);
+    Py_ssize_t errind = -1;
+    Py_BEGIN_CRITICAL_SECTION(self);
+    errind = find_bit(self, 0, 0, self->nbits, 0);
+    Py_END_CRITICAL_SECTION();
+    return PyBool_FromLong( errind == -1);
 }
 
 PyDoc_STRVAR(all_doc,
@@ -978,7 +982,11 @@ Note that `a.all()` is faster than `all(a)`.");
 static PyObject *
 bitarray_any(bitarrayobject *self)
 {
-    return PyBool_FromLong(find_bit(self, 1, 0, self->nbits, 0) >= 0);
+    Py_ssize_t errind = -1;
+    Py_BEGIN_CRITICAL_SECTION(self);
+    errind = find_bit(self, 1, 0, self->nbits, 0);
+    Py_END_CRITICAL_SECTION();
+    return PyBool_FromLong(errind >= 0);
 }
 
 PyDoc_STRVAR(any_doc,
@@ -1000,7 +1008,9 @@ bitarray_append(bitarrayobject *self, PyObject *value)
 
     if (resize(self, self->nbits + 1) < 0)
         return NULL;
+    Py_BEGIN_CRITICAL_SECTION(self);
     setbit(self, self->nbits - 1, vi);
+    Py_END_CRITICAL_SECTION();
     Py_RETURN_NONE;
 }
 
@@ -1343,7 +1353,9 @@ bitarray_invert(bitarrayobject *self, PyObject *args)
             PyErr_SetString(PyExc_IndexError, "index out of range");
             return NULL;
         }
+        Py_BEGIN_CRITICAL_SECTION(self);
         self->ob_item[i / 8] ^= BITMASK(self, i);
+        Py_END_CRITICAL_SECTION();
         Py_RETURN_NONE;
     }
     if (PySlice_Check(arg)) {
@@ -1352,12 +1364,18 @@ bitarray_invert(bitarrayobject *self, PyObject *args)
         if (PySlice_GetIndicesEx(arg, self->nbits,
                                  &start, &stop, &step, &slicelength) < 0)
             return NULL;
+        Py_BEGIN_CRITICAL_SECTION(self);
         adjust_step_positive(slicelength, &start, &stop, &step);
+        Py_END_CRITICAL_SECTION();
+        Py_BEGIN_CRITICAL_SECTION(self);
         invert_range(self, start, stop, step);
+        Py_END_CRITICAL_SECTION();
         Py_RETURN_NONE;
     }
     if (arg == Py_None) {
+        Py_BEGIN_CRITICAL_SECTION(self);
         invert_span(self, 0, self->nbits);
+        Py_END_CRITICAL_SECTION();
         Py_RETURN_NONE;
     }
 
@@ -4335,5 +4353,9 @@ PyInit__bitarray(void)
     PyModule_AddObject(m, "__version__",
                        PyUnicode_FromString(BITARRAY_VERSION));
 
+#ifdef Py_GIL_DISABLED
+    PyUnstable_Module_SetGIL(m, Py_MOD_GIL_NOT_USED);
+#endif
+
     return m;
 }
diff --git a/bitarray/_util.c b/bitarray/_util.c
index 84abe26a2..48f64c5a1 100644
--- a/bitarray/_util.c
+++ b/bitarray/_util.c
@@ -2105,5 +2105,9 @@ PyInit__util(void)
     PyModule_AddObject(m, "_SEGSIZE", PyLong_FromSsize_t(SEGSIZE));
 #endif
 
+#ifdef Py_GIL_DISABLED
+    PyUnstable_Module_SetGIL(m, Py_MOD_GIL_NOT_USED);
+#endif
+
     return m;
 }