diff --git a/cylc/flow/task_pool.py b/cylc/flow/task_pool.py
index 52ddbddc78c..8697c74d5d8 100644
--- a/cylc/flow/task_pool.py
+++ b/cylc/flow/task_pool.py
@@ -800,7 +800,7 @@ def reload_taskdefs(self) -> None:
                     # Keep active orphaned task, but stop it from spawning.
                     itask.graph_children = {}
                     LOG.warning(
-                        "f[{itask}] will not spawn children "
+                        f"[{itask}] will not spawn children "
                         "- task definition removed"
                     )
             else: