diff --git a/Documentation/security/credentials.rst b/Documentation/security/credentials.rst
index 66a2e24939d8..5bb7125faeee 100644
--- a/Documentation/security/credentials.rst
+++ b/Documentation/security/credentials.rst
@@ -451,6 +451,13 @@ checks and hooks done.  Both the current and the proposed sets of credentials
 are available for this purpose as current_cred() will return the current set
 still at this point.
 
+When replacing the group list, the new list must be sorted before it
+is added to the credential, as a binary search is used to test for
+membership.  In practice, this means :c:func:`groups_sort` should be
+called before :c:func:`set_groups` or :c:func:`set_current_groups`.
+:c:func:`groups_sort)` must not be called on a ``struct group_list`` which
+is shared as it may permute elements as part of the sorting process
+even if the array is already sorted.
 
 When the credential set is ready, it should be committed to the current process
 by calling::