diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-10-12-11-00-06.gh-issue-139988.4wi51t.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-12-11-00-06.gh-issue-139988.4wi51t.rst
new file mode 100644
index 00000000000000..60fa3b1d339cb1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-12-11-00-06.gh-issue-139988.4wi51t.rst
@@ -0,0 +1,2 @@
+Fix a memory leak when failing to create a :class:`~typing.Union` type.
+Patch by Bénédikt Tran.
diff --git a/Objects/unionobject.c b/Objects/unionobject.c
index 2206ed80ef03fd..c4ece0fe09f018 100644
--- a/Objects/unionobject.c
+++ b/Objects/unionobject.c
@@ -474,11 +474,13 @@ _Py_union_from_tuple(PyObject *args)
     }
     if (PyTuple_CheckExact(args)) {
         if (!unionbuilder_add_tuple(&ub, args)) {
+            unionbuilder_finalize(&ub);
             return NULL;
         }
     }
     else {
         if (!unionbuilder_add_single(&ub, args)) {
+            unionbuilder_finalize(&ub);
             return NULL;
         }
     }