diff --git a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
index 01e53e1be022096da706385667f241cc3ba1f914..1e06ed2893d358dfd3f6fb1f962eb3b33234e415 100644
--- a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
+++ b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
@@ -2238,7 +2238,7 @@ def _generate_subtask_specs_from_pulsar_pipeline_task_specs(pipeline_task_specs,
     subtask_specs["dspsr"]["digifil_extra_opts"]   = " ".join([
               "-D {dm}".format(**digifil_specs) if digifil_specs["dm"] != -1 else "",
               "-t {integration_time}".format(**digifil_specs),
-              "-f {frequency_channels}{dedispersion}".format(**digifil_specs, dedispersion=":D" if digifil_specs["coherent_dedispersion"] else ""),
+              "-F {frequency_channels}{dedispersion}".format(**digifil_specs, dedispersion=":D" if digifil_specs["coherent_dedispersion"] else ""),
               ])
 
     subtask_specs["dspsr"]["nopdmp"]               = not dspsr_specs["optimise_period_dm"]