also decref the right thing
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index e152e73..9a9703a 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -9140,7 +9140,7 @@
         return -1;
     }
     if (PyUnicode_READY(sub_obj) == -1 || PyUnicode_READY(str_obj) == -1) {
-        Py_DECREF(substr);
+        Py_DECREF(sub_obj);
         Py_DECREF(str_obj);
         return -1;
     }