diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.a3cc5d.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.a3cc5d.rst
new file mode 100644
index 00000000000000..69c53e84e216b3
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.a3cc5d.rst
@@ -0,0 +1 @@
+Fix a crash when constructing an error for invalid generic alias arguments.
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index ddee7957178f48..5649866cc50234 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -546,13 +546,13 @@ _Py_subs_parameters(PyObject *self, PyObject *args, PyObject *parameters, PyObje
         }
         if (unpack) {
             if (!PyTuple_Check(arg)) {
-                Py_DECREF(newargs);
-                Py_DECREF(item);
-                Py_XDECREF(tuple_args);
                 PyObject *original = PyTuple_GET_ITEM(args, iarg);
                 PyErr_Format(PyExc_TypeError,
                              "expected __typing_subst__ of %T objects to return a tuple, not %T",
                              original, arg);
+                Py_DECREF(newargs);
+                Py_DECREF(item);
+                Py_XDECREF(tuple_args);
                 Py_DECREF(arg);
                 return NULL;
             }