diff --git a/golem/core/processmonitor.py b/golem/core/processmonitor.py
index 771704766b..ddbb234167 100644
--- a/golem/core/processmonitor.py
+++ b/golem/core/processmonitor.py
@@ -87,9 +87,9 @@ def kill_process(cls, process):
                 elif isinstance(process, Process):
                     process.join()
             except Exception as exc:
-                logger.error("Error terminating process %d: %r", process, exc)
+                logger.error("Error terminating process %s: %r", process, exc)
             else:
-                logger.warning("Subprocess %d terminated", cls._pid(process))
+                logger.warning("Subprocess %s terminated", cls._pid(process))
 
     @staticmethod
     def _pid(process):