diff --git a/Misc/NEWS.d/next/Core and Builtins/2025-02-05-11-29-52.gh-issue-129643.4mGzvg.rst b/Misc/NEWS.d/next/Core and Builtins/2025-02-05-11-29-52.gh-issue-129643.4mGzvg.rst
new file mode 100644
index 00000000000000..420e1fb9781ff3
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2025-02-05-11-29-52.gh-issue-129643.4mGzvg.rst	
@@ -0,0 +1 @@
+Fix thread safety of :c:func:`PyList_Insert` in free-threading builds.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index d581fc8b0b290c..65a8b06d978df4 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -498,8 +498,8 @@ ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
         where = n;
     items = self->ob_item;
     for (i = n; --i >= where; )
-        items[i+1] = items[i];
-    items[where] = Py_NewRef(v);
+        FT_ATOMIC_STORE_PTR_RELAXED(items[i+1], items[i]);
+    FT_ATOMIC_STORE_PTR_RELEASE(items[where], Py_NewRef(v));
     return 0;
 }