diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 48dd42ca3c..f9c3f41890 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -226,7 +226,12 @@
specified user and group must have been created statically in the user database no later than the moment the
service is started, for example using the
sysusers.d5 facility, which
- is applied at boot or package install time.
+ is applied at boot or package install time.
+
+ If the User= setting is used the supplementary group list is initialized
+ from the specified user's default group list, as defined in the system's user and group
+ database. Additional groups may be configured through the SupplementaryGroups=
+ setting (see below).