diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-08-01-19-17-56.gh-issue-155053.sxmlTO.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-08-01-19-17-56.gh-issue-155053.sxmlTO.rst
new file mode 100644
index 00000000000000..d96566f8776574
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-08-01-19-17-56.gh-issue-155053.sxmlTO.rst
@@ -0,0 +1,2 @@
+Fix a crash in :class:`types.GenericAlias` during substitution of a
+``TypeVarTuple`` under allocation failure.
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index 2633b9af81c5b9..b7df689a8a674f 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -303,6 +303,7 @@ subs_tvars(PyObject *obj, PyObject *params,
                                     PyTuple_GET_SIZE(arg));
                     if (j < 0) {
                         Py_DECREF(subparams);
+                        /* tuple_extend() clears subargs on failure. */
                         assert(subargs == NULL);
                         return NULL;
                     }