diff --git a/FDTD/operator_cylindermultigrid.cpp b/FDTD/operator_cylindermultigrid.cpp
index e78e4d7..5483567 100644
--- a/FDTD/operator_cylindermultigrid.cpp
+++ b/FDTD/operator_cylindermultigrid.cpp
@@ -34,6 +34,11 @@ Operator_CylinderMultiGrid::~Operator_CylinderMultiGrid()
 
 Operator_CylinderMultiGrid* Operator_CylinderMultiGrid::New(vector<double> Split_Radii, unsigned int numThreads)
 {
+	if ((Split_Radii.size()==0) || (Split_Radii.size()>CYLIDINDERMULTIGRID_LIMIT))
+	{
+		cerr << "Operator_CylinderMultiGrid::New: Warning: Number of multigrids invalid! Split-Number: " << Split_Radii.size() << endl;
+		return NULL;
+	}
 	cout << "Create cylindrical multi grid FDTD operator " << endl;
 	Operator_CylinderMultiGrid* op = new Operator_CylinderMultiGrid(Split_Radii);
 	op->setNumThreads(numThreads);
diff --git a/FDTD/operator_cylindermultigrid.h b/FDTD/operator_cylindermultigrid.h
index 6e7a147..ade2c82 100644
--- a/FDTD/operator_cylindermultigrid.h
+++ b/FDTD/operator_cylindermultigrid.h
@@ -18,6 +18,8 @@
 #ifndef OPERATOR_CYLINDERMULTIGRID_H
 #define OPERATOR_CYLINDERMULTIGRID_H
 
+#define CYLIDINDERMULTIGRID_LIMIT 20
+
 #include "operator_cylinder.h"
 
 //! This is a cylindrical FDTD operator using a simple multi-grid approach.
diff --git a/openems.cpp b/openems.cpp
index 14849aa..a31e07b 100644
--- a/openems.cpp
+++ b/openems.cpp
@@ -457,6 +457,8 @@ bool openEMS::SetupOperator(TiXmlElement* FDTD_Opts)
 		{
 			string rad(radii);
 			FDTD_Op = Operator_CylinderMultiGrid::New(SplitString2Double(rad,','),m_engine_numThreads);
+			if (FDTD_Op==NULL)
+				FDTD_Op = Operator_Cylinder::New(m_engine_numThreads);
 		}
 		else
 			FDTD_Op = Operator_Cylinder::New(m_engine_numThreads);