Issue #21778: Clarify use of flags if PyBuffer_FillInfo() is used inside a
getbufferproc().
diff --git a/Doc/c-api/buffer.rst b/Doc/c-api/buffer.rst
index a7de37e..230c6a9 100644
--- a/Doc/c-api/buffer.rst
+++ b/Doc/c-api/buffer.rst
@@ -489,8 +489,8 @@
:c:member:`view->obj` to *NULL* and return -1;
If this function is used as part of a :ref:`getbufferproc <buffer-structs>`,
- *exporter* MUST be set to the exporting object. Otherwise, *exporter* MUST
- be NULL.
+ *exporter* MUST be set to the exporting object and *flags* must be passed
+ unmodified. Otherwise, *exporter* MUST be NULL.