diff --git a/cylc/flow/task_pool.py b/cylc/flow/task_pool.py
index 38d4a5e3a9c..d4a87c82570 100644
--- a/cylc/flow/task_pool.py
+++ b/cylc/flow/task_pool.py
@@ -1398,8 +1398,11 @@ def force_trigger_tasks(
                 or self._get_hidden_task_by_id(task_id)
             )
             if itask is None:
-                # Spawn with new flow number.
-                flow_nums = {self.flow_mgr.get_new_flow(flow_descr)}
+                # Spawn with new flow number, unless no reflow.
+                if reflow:
+                    flow_nums = {self.flow_mgr.get_new_flow(flow_descr)}
+                else:
+                    flow_nums = set()
                 itask = self.spawn_task(name, point, flow_nums)
                 if itask is None:
                     continue
diff --git a/tests/functional/spawn-on-demand/10-retrigger/flow.cylc b/tests/functional/spawn-on-demand/10-retrigger/flow.cylc
index 73dd23ae388..d0b614bf5b0 100644
--- a/tests/functional/spawn-on-demand/10-retrigger/flow.cylc
+++ b/tests/functional/spawn-on-demand/10-retrigger/flow.cylc
@@ -18,7 +18,8 @@
       """
    [[triggerer]]
       script = """
-         cylc__job__poll_grep_workflow_log '\[oops\.1\].* (received)failed'
+         cylc__job__poll_grep_workflow_log -E \
+            'oops\.1 running .* \(received\)failed'
          cylc trigger ${CYLC_WORKFLOW_NAME} oops.1
        """
    [[foo, bar]]