diff --git a/man2/prctl.2 b/man2/prctl.2
index d26e6aee5..811e08396 100644
--- a/man2/prctl.2
+++ b/man2/prctl.2
@@ -105,6 +105,12 @@ This operation requires setting
 .I arg3
 to zero.
 .RE
+.IP
+In all of the above operations,
+.I arg4
+and
+.I arg5
+must be specified as 0.
 .TP
 .BR PR_CAPBSET_READ " (since Linux 2.6.25)"
 Return (as the function result) 1 if the capability specified in