Note that the caller is resposible for freeing the result of PyOS_double_to_string.
diff --git a/Doc/c-api/conversion.rst b/Doc/c-api/conversion.rst
index 51bc44b..4d1f42f 100644
--- a/Doc/c-api/conversion.rst
+++ b/Doc/c-api/conversion.rst
@@ -109,7 +109,8 @@
*val* is a finite number, an infinite number, or not a number, respectively.
The return value is a pointer to *buffer* with the converted string or
- *NULL* if the conversion failed.
+ *NULL* if the conversion failed. The caller is responsible for freeing the
+ returned string by calling :cfunc:`PyMem_Free`.
.. versionadded:: 2.7