diff --git a/Common/processmodematch.cpp b/Common/processmodematch.cpp
index 620257d..85d2d58 100644
--- a/Common/processmodematch.cpp
+++ b/Common/processmodematch.cpp
@@ -174,7 +174,7 @@ void ProcessModeMatch::InitProcess()
 			for (int n=0; n<2; ++n)
 			{
 				m_ModeDist[n][posP][posPP] = m_ModeParser[n]->Eval(var); //calc mode template
-				if ((isnan(m_ModeDist[n][posP][posPP])) || (isinf(m_ModeDist[n][posP][posPP])))
+				if ((std::isnan(m_ModeDist[n][posP][posPP])) || (std::isinf(m_ModeDist[n][posP][posPP])))
 					m_ModeDist[n][posP][posPP] = 0.0;
 				norm += pow(m_ModeDist[n][posP][posPP],2) * area;
 			}
diff --git a/FDTD/extensions/operator_ext_tfsf.cpp b/FDTD/extensions/operator_ext_tfsf.cpp
index 663dc1f..62fd580 100644
--- a/FDTD/extensions/operator_ext_tfsf.cpp
+++ b/FDTD/extensions/operator_ext_tfsf.cpp
@@ -159,7 +159,7 @@ bool Operator_Ext_TFSF::BuildExtension()
 		else
 			m_PhVel=m_Op->CalcNumericPhaseVelocity(m_Start,m_Stop,m_PropDir,m_Frequency);
 
-		if ((m_PhVel<0) || (m_PhVel>__C0__/ref_index) || isnan(m_PhVel))
+		if ((m_PhVel<0) || (m_PhVel>__C0__/ref_index) || std::isnan(m_PhVel))
 		{
 			cerr << "Operator_Ext_TFSF::BuildExtension: Warning, invalid phase velocity found, resetting to c0! " << endl;
 			m_PhVel = __C0__/ref_index;
diff --git a/FDTD/operator.cpp b/FDTD/operator.cpp
index a7582aa..259b1fb 100644
--- a/FDTD/operator.cpp
+++ b/FDTD/operator.cpp
@@ -1395,7 +1395,7 @@ bool Operator::AverageMatCellCenter(int ny, const unsigned int* pos, double* Eff
 	if (EffMat[3]) EffMat[3]=length / EffMat[3];
 
 	for (int n=0; n<4; ++n)
-		if (isnan(EffMat[n]) || isinf(EffMat[n]))
+		if (std::isnan(EffMat[n]) || std::isinf(EffMat[n]))
 		{
 			cerr << "Operator::" << __func__ << ": Error, an effective material parameter is not a valid result, this should NOT have happend... exit..." << endl;
 			cerr << ny << "@" << n << " : " << pos[0] << "," << pos[1] << ","  << pos[2] << endl;
@@ -1508,7 +1508,7 @@ bool Operator::AverageMatQuarterCell(int ny, const unsigned int* pos, double* Ef
 	if (EffMat[3]) EffMat[3]=length / EffMat[3];
 
 	for (int n=0; n<4; ++n)
-		if (isnan(EffMat[n]) || isinf(EffMat[n]))
+		if (std::isnan(EffMat[n]) || std::isinf(EffMat[n]))
 		{
 			cerr << "Operator::" << __func__ << ": Error, An effective material parameter is not a valid result, this should NOT have happend... exit..." << endl;
 			cerr << ny << "@" << n << " : " << pos[0] << "," << pos[1] << ","  << pos[2] << endl;
@@ -1555,7 +1555,7 @@ bool Operator::Calc_LumpedElements()
 				if (R<0)
 					R = NAN;
 
-				if ((isnan(R)) && (isnan(C)))
+				if ((std::isnan(R)) && (std::isnan(C)))
 				{
 					cerr << "Operator::Calc_LumpedElements(): Warning: Lumped Element R or C not specified! skipping. "
 							<< " ID: " << prims.at(bn)->GetID() << " @ Property: " << PLE->GetName() << endl;
diff --git a/tools/sar_calculation.cpp b/tools/sar_calculation.cpp
index 343aa07..e135aca 100644
--- a/tools/sar_calculation.cpp
+++ b/tools/sar_calculation.cpp
@@ -292,7 +292,7 @@ int SAR_Calculation::FindFittingCubicalMass(unsigned int pos[3], float box_size,
 bool SAR_Calculation::GetCubicalMass(unsigned int pos[3], double box_size, unsigned int start[3], unsigned int stop[3],
 									 float partial_start[3], float partial_stop[3], double &mass, double &volume, double &bg_ratio, int disabledFace)
 {
-	if ((box_size<=0) || isnan(box_size) || isinf(box_size))
+	if ((box_size<=0) || std::isnan(box_size) || std::isinf(box_size))
 	{
 		cerr << "SAR_Calculation::GetCubicalMass: critical error: invalid averaging box size!! EXIT" << endl;
 		exit(-1);