diff --git a/NPLib/Detectors/CsI/TCsIPhysics.cxx b/NPLib/Detectors/CsI/TCsIPhysics.cxx
index cb9410b88262fb2197ca5ff0a9b6043737f32097..1384ec8a06f86f1cb818b7e2d6d272abd7d2e8e0 100644
--- a/NPLib/Detectors/CsI/TCsIPhysics.cxx
+++ b/NPLib/Detectors/CsI/TCsIPhysics.cxx
@@ -33,6 +33,7 @@
 #include <fstream>
 #include <limits>
 #include <stdlib.h>
+#include <cmath>
 using namespace std;
 
 //   ROOT