diff --git a/man2/killpg.2 b/man2/killpg.2
index 89a806249..6b53ca168 100644
--- a/man2/killpg.2
+++ b/man2/killpg.2
@@ -113,6 +113,11 @@ returned when the permission check failed for at least one target process,
 while POSIX documents
 .B EPERM
 only when the permission check failed for all target processes.
+
+On Linux,
+.BR killpg ()
+is implemented as a library function that makes the call
+.IR "kill(-pgrp,\ sig)" .
 .SH "SEE ALSO"
 .BR getpgrp (2),
 .BR kill (2),