diff --git a/lib/libnetgraph/netgraph.3 b/lib/libnetgraph/netgraph.3
index feff469bde3..bf2de910426 100644
--- a/lib/libnetgraph/netgraph.3
+++ b/lib/libnetgraph/netgraph.3
@@ -170,6 +170,9 @@ is non-NULL, it must point to a buffer of at least
 bytes, which will be filled in (and NUL terminated) with the path to
 the node from which the message was received.
 .Pp
+The length of the control message is returned.
+A return value of zero indicates that the socket was closed.
+.Pp
 .Fn NgRecvAsciiMsg
 works exactly like
 .Fn NgRecvMsg ,
@@ -206,6 +209,9 @@ is non-NULL, it must point to a buffer of at least
 bytes, which will be filled in (and NUL terminated) with the name of
 the hook on which the data was received.
 .Pp
+The length of the packet is returned.
+A return value of zero indicates that the socket was closed.
+.Pp
 .Fn NgSetDebug
 and
 .Fn NgSetErrLog