diff --git a/MagneticField/MagFieldUtils/src/MagFieldTestbedAlg.cxx b/MagneticField/MagFieldUtils/src/MagFieldTestbedAlg.cxx
index 4c212670c62ef8325a0198f641cad42ac529faa6..537786e22d980f0c6957d8bfc7dc4748a4ef8be2 100644
--- a/MagneticField/MagFieldUtils/src/MagFieldTestbedAlg.cxx
+++ b/MagneticField/MagFieldUtils/src/MagFieldTestbedAlg.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 */
 
 ///////////////////////////////////////////////////////////////////
@@ -39,12 +39,15 @@
 // performance test
 #include <time.h>
 #include <vector>
+#include <cmath> // isnan
 
 namespace {
 const double solenoidRadius = 1075.;
 const double solenoidZhalf = 2820.;
 }
 
+using std::isnan;
+
 ///////////////////////////////////////////////////////////////////
 // Public methods:
 ///////////////////////////////////////////////////////////////////