diff --git a/parsl/monitoring/monitoring.py b/parsl/monitoring/monitoring.py
index <HASH>..<HASH> 100644
--- a/parsl/monitoring/monitoring.py
+++ b/parsl/monitoring/monitoring.py
@@ -261,7 +261,7 @@ class MonitoringHub(RepresentationMixin):
 
         if isinstance(comm_q_result, str):
             self.logger.error(f"MonitoringRouter sent an error message: {comm_q_result}")
-            raise RuntimeError("MonitoringRouter failed to start: {comm_q_result}")
+            raise RuntimeError(f"MonitoringRouter failed to start: {comm_q_result}")
 
         udp_dish_port, ic_port = comm_q_result
Add missing f for an f-string (#<I>)