diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-05-07-16-57-56.gh-issue-118561.wNMKVd.rst b/Misc/NEWS.d/next/Core and Builtins/2024-05-07-16-57-56.gh-issue-118561.wNMKVd.rst
new file mode 100644
index 000000000000000..aca1dd8f2d52a9a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2024-05-07-16-57-56.gh-issue-118561.wNMKVd.rst	
@@ -0,0 +1,2 @@
+Fix race condition in free-threaded build where ``list.extend`` could expose
+uninitialied memory to concurrent readers.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 3c4e2d2e6ed7ded..8bd8544de4bd016 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -192,6 +192,7 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
         return -1;
     }
     items = array->ob_item;
+    memset(items, 0, size * sizeof(PyObject *));
 #else
     items = PyMem_New(PyObject*, size);
     if (items == NULL) {