diff --git a/erp5/util/benchmark/process.py b/erp5/util/benchmark/process.py
index b23d8514ac68aa77019425dee2066ad16c9c2a53..f879aef83bb5e734596aaad9cf561d7ee7bc7ca6 100644
--- a/erp5/util/benchmark/process.py
+++ b/erp5/util/benchmark/process.py
@@ -145,7 +145,7 @@ class BenchmarkProcess(multiprocessing.Process):
       self._logger.error(e)
 
     except BaseException, e:
-      exit_msg = e
+      exit_msg = str(e)
       exit_status = 1
 
     self._exit_msg_queue.put(exit_msg)