diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 0722312..2c8378e 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -13320,6 +13320,7 @@
         Py_DECREF(writer->buffer);
         return NULL;
     }
+    assert(_PyUnicode_CheckConsistency(writer->buffer, 1));
     return writer->buffer;
 }