diff --git a/include/tug/Core/BTCS.hpp b/include/tug/Core/BTCS.hpp
index 4ee01ed..73a312b 100644
--- a/include/tug/Core/BTCS.hpp
+++ b/include/tug/Core/BTCS.hpp
@@ -138,10 +138,9 @@ template <typename T>
 constexpr T calcExplicitConcentrationsBoundaryConstant(T conc_center, T conc_bc,
                                                        T alpha_center,
                                                        T alpha_neighbor, T sy) {
-  return sy * calcAlphaIntercell(alpha_center, alpha_neighbor) * conc_center +
-         (1 - sy * (calcAlphaIntercell(alpha_center, alpha_center) +
-                    alpha_center)) *
-             conc_center +
+  const T inter_cell = calcAlphaIntercell(alpha_center, alpha_neighbor);
+  return sy * inter_cell * conc_center +
+         (1 - sy * (inter_cell + alpha_center)) * conc_center +
          sy * alpha_center * conc_bc;
 }