diff --git a/FDTD/engine_interface_fdtd.cpp b/FDTD/engine_interface_fdtd.cpp
index c81b811..ec8c326 100644
--- a/FDTD/engine_interface_fdtd.cpp
+++ b/FDTD/engine_interface_fdtd.cpp
@@ -199,7 +199,7 @@ double* Engine_Interface_FDTD::GetRawInterpolatedDualField(const unsigned int* p
 
 double Engine_Interface_FDTD::CalcVoltageIntegral(const unsigned int* start, const unsigned int* stop) const
 {
-	if ((start[0]!=stop[0] + start[1]!=stop[1] + start[2]!=stop[2])!=1)
+	if (((start[0]!=stop[0]) + (start[1]!=stop[1]) + (start[2]!=stop[2]))!=1)
 	{
 		cerr << "Engine_Interface_FDTD::CalcVoltageIntegral: Error, only a 1D/line integration is allowed" << endl;
 		return 0;