diff --git a/cylc/flow/task_job_mgr.py b/cylc/flow/task_job_mgr.py
index e41e05dfd30..2b7da27e4d5 100644
--- a/cylc/flow/task_job_mgr.py
+++ b/cylc/flow/task_job_mgr.py
@@ -979,8 +979,8 @@ def _set_retry_timers(
             rtconfig = itask.tdef.rtconfig
 
         submit_delays = (
-            rtconfig['submission retry delays']
-            or itask.platform['submission retry delays']
+            rtconfig.get('submission retry delays', [])
+            or itask.platform.get('submission retry delays', [])
         )
 
         for key, delays in [