diff --git a/doc/tcpkali.1 b/doc/tcpkali.1
index 876213c..7771e8e 100644
--- a/doc/tcpkali.1
+++ b/doc/tcpkali.1
@@ -296,7 +296,7 @@ T}
 T{
 message.marker
 T}@T{
-Indicate a message boundary for latency measurement.
+Produce a message timestamp for message rate and latency measurements.
 T}
 T{
 ws.continuation, ws.ping, ws.pong, ws.text, ws.binary
@@ -369,6 +369,16 @@ Mean and maximum values can be reported using
 Default is \f[C]95,99,99.5\f[].
 .RS
 .RE
+.TP
+.B \-\-message\-marker
+Passive mode detection or message markers.
+Given this option, tcpkali will detect the \\{message.marker} byte
+sequences and will calculate message rate (in messages per second) and
+message arrival latency.
+In the active mode, message rate calculation is implicitly enabled by
+using the \\{message.marker} expression.
+.RS
+.RE
 .SS STATSD OPTIONS
 .TP
 .B \-\-statsd
diff --git a/doc/tcpkali.man.md b/doc/tcpkali.man.md
index c39683d..48c92a3 100644
--- a/doc/tcpkali.man.md
+++ b/doc/tcpkali.man.md
@@ -174,7 +174,8 @@ Expression          Description
 
  re                 Randomized expression, for each message.
 
- message.marker     Indicate a message boundary for latency measurement.
+ message.marker     Produce a message timestamp for message rate and latency
+                    measurements.
 
  ws.continuation,   Specify WebSocket frame types.
  ws.ping, ws.pong,  Refer to RFC 6455, section 11.8.
@@ -225,6 +226,13 @@ and the time the latency marker is observed in the downstream traffic
     Mean and maximum values can be reported using **--latency-percentiles 50,100**.
     Default is `95,99,99.5`.
 
+--message-marker
+:   Passive mode detection or message markers. Given this option, tcpkali
+    will detect the \\{message.marker} byte sequences and will calculate
+    message rate (in messages per second) and message arrival latency.
+    In the active mode, message rate calculation is implicitly enabled by
+    using the \\{message.marker} expression.
+
 ## STATSD OPTIONS
 
 --statsd