diff --git a/loky/process_executor.py b/loky/process_executor.py
index 1e08cc21..b89d31af 100644
--- a/loky/process_executor.py
+++ b/loky/process_executor.py
@@ -192,7 +192,7 @@ def _python_exit():
     items = list(_threads_wakeups.items())
     if len(items) > 0:
         mp.util.debug(
-            "Interpreter shutting down. Waking up {len(items)}"
+            f"Interpreter shutting down. Waking up {len(items)}"
             f"executor_manager_thread:\n{items}"
         )