diff --git a/Statistic.h b/Statistic.h
index ae34cb4..55d1365 100644
--- a/Statistic.h
+++ b/Statistic.h
@@ -38,12 +38,12 @@ public:
 
 
 protected:
-  uint32_t _cnt;
-  float    _sum;
-  float    _min;
-  float    _max;
-  bool     _useStdDev;
-  float    _ssqdif;    // sum of squares difference
+  volatile uint32_t _cnt;
+  volatile float    _sum;
+  volatile float    _min;
+  volatile float    _max;
+  volatile bool     _useStdDev;
+  volatile float    _ssqdif;    // sum of squares difference
 
 };