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