diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 8ceb3f32b8b..29404c3c262 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1215,6 +1215,8 @@ PyUnicode_AsWideCharString(PyUnicodeObject *unicode,
         return NULL;
     }
     unicode_aswidechar(unicode, buffer, buflen);
+    if (size)
+        *size = buflen;
     return buffer;
 }