diff --git a/config.c b/config.c
index ee0f302..934caa2 100644
--- a/config.c
+++ b/config.c
@@ -534,6 +534,8 @@ static enum parser_result parse_global_setting(const char *option,
 			cfg->clock_servo = CLOCK_SERVO_LINREG;
 		else if (!strcasecmp("ntpshm", value))
 			cfg->clock_servo = CLOCK_SERVO_NTPSHM;
+		else if (!strcasecmp("nullf", value))
+			cfg->clock_servo = CLOCK_SERVO_NULLF;
 		else
 			return BAD_VALUE;
 
diff --git a/ptp4l.8 b/ptp4l.8
index caeb805..0bdccb1 100644
--- a/ptp4l.8
+++ b/ptp4l.8
@@ -318,11 +318,13 @@ generated by the master.
 The default is 0 (disabled).
 .TP
 .B clock_servo
-The servo which is used to synchronize the local clock. Valid values are pi for
-a PI controller, linreg for an adaptive controller using linear regression, and
-ntpshm for the NTP SHM reference clock to allow another process to synchronize
-the local clock (the SHM segment number is set to the domain number).
-The default is pi.
+The servo which is used to synchronize the local clock. Valid values
+are "pi" for a PI controller, "linreg" for an adaptive controller
+using linear regression, "ntpshm" for the NTP SHM reference clock to
+allow another process to synchronize the local clock (the SHM segment
+number is set to the domain number), and "nullf" for a servo that
+always dials frequency offset zero (for use in SyncE nodes).
+The default is "pi."
 .TP
 .B pi_proportional_const
 The proportional constant of the PI controller. When set to 0.0, the