diff --git a/sourcestats.c b/sourcestats.c
index 2d28aff..1e1a9ef 100644
--- a/sourcestats.c
+++ b/sourcestats.c
@@ -724,7 +724,7 @@ SST_GetTrackingData(SST_Stats inst, struct timespec *ref_time,
   *root_delay = inst->root_delays[j];
 
   elapsed_sample = UTI_DiffTimespecsToDouble(&inst->offset_time, &inst->sample_times[i]);
-  *root_dispersion = inst->root_dispersions[j] + inst->skew * elapsed_sample;
+  *root_dispersion = inst->root_dispersions[j] + inst->skew * elapsed_sample + *offset_sd;
 
   DEBUG_LOG("n=%d freq=%f (%.3fppm) skew=%f (%.3fppm) avoff=%f offsd=%f disp=%f",
             inst->n_samples, *frequency, 1.0e6* *frequency, *skew, 1.0e6* *skew,