diff --git a/ProcessLib/RichardsMechanics/IntegrationPointData.h b/ProcessLib/RichardsMechanics/IntegrationPointData.h
index d7558186d89d5cd6f929f83262188dda87f4888b..d8442413c26cbb5cffa8b3614b2f86a856beca11 100644
--- a/ProcessLib/RichardsMechanics/IntegrationPointData.h
+++ b/ProcessLib/RichardsMechanics/IntegrationPointData.h
@@ -56,6 +56,8 @@ struct IntegrationPointData final
     typename ShapeMatricesTypePressure::GlobalDimNodalMatrixType dNdx_p;
 
     double saturation;
+    double porosity = std::numeric_limits<double>::quiet_NaN();
+    double porosity_prev = std::numeric_limits<double>::quiet_NaN();
 
     MaterialLib::Solids::MechanicsBase<DisplacementDim> const& solid_material;
     std::unique_ptr<typename MaterialLib::Solids::MechanicsBase<
@@ -67,6 +69,7 @@ struct IntegrationPointData final
     {
         eps_prev = eps;
         sigma_eff_prev = sigma_eff;
+        porosity_prev = porosity;
         material_state_variables->pushBackState();
     }