diff --git a/avogadro/calc/chargemodel.cpp b/avogadro/calc/chargemodel.cpp
index f3fc749a4c..0611a19d75 100644
--- a/avogadro/calc/chargemodel.cpp
+++ b/avogadro/calc/chargemodel.cpp
@@ -16,7 +16,7 @@ using Core::Molecule;
 namespace Calc {
 
 #ifndef M_PI
-#define M_PI 3.14159265358979323846
+constexpr double M_PI = 3.14159265358979323846;
 #endif
 
 ChargeModel::ChargeModel() : m_dielectric(1.0) {}