diff --git a/sisyphus/simple_linux_utility_for_resource_management_engine.py b/sisyphus/simple_linux_utility_for_resource_management_engine.py
index d5a5e29..0c61290 100644
--- a/sisyphus/simple_linux_utility_for_resource_management_engine.py
+++ b/sisyphus/simple_linux_utility_for_resource_management_engine.py
@@ -233,7 +233,7 @@ def submit_helper(self, call, logpath, rqmt, name, task_name, start_id, end_id,
         :param int step_size:
         """
         name = self.process_task_name(name)
-        out_log_file = logpath + "/%x.%A.%a"
+        out_log_file = f"{logpath}/%x.%A.%a"
         if rqmt.get("multi_node_slots", 1) > 1:
             out_log_file += ".%t"
         sbatch_call = ["sbatch", "-J", name, "--mail-type=None"]