diff --git a/openquake/engine/performance.py b/openquake/engine/performance.py
index <HASH>..<HASH> 100644
--- a/openquake/engine/performance.py
+++ b/openquake/engine/performance.py
@@ -204,7 +204,7 @@ class EnginePerformanceMonitor(PerformanceMonitor):
         is intended for debugging purposes.
         """
         if no_distribute():
-            logs.LOG.warn('PyMem: %d mb, PgMem: %d mb' % self.mem_peaks)
+            logs.LOG.warn('PyMem: %s mb, PgMem: %s mb' % self.mem_peaks)
 
     def __exit__(self, etype, exc, tb):
         super(EnginePerformanceMonitor, self).__exit__(etype, exc, tb)
Fixed an error happening when the memory stats are not available (None instead of an integer)


Former-commit-id: <I>cbd<I>c<I>f4c7ba4dd<I>d8d2b0fdd