diff --git a/julia/TUG/src/Core/BTCS.jl b/julia/TUG/src/Core/BTCS.jl
index ecbca66..dd9b8af 100644
--- a/julia/TUG/src/Core/BTCS.jl
+++ b/julia/TUG/src/Core/BTCS.jl
@@ -73,7 +73,7 @@ function calcExplicitConcentrationsBoundaryConstant(
         calcAlphaIntercell(alpha_center, alpha_center)
 
     return sy * alpha_center_neighbor * conc_center +
-           (1 - sy * (alpha_center_center + 2 * alpha_center)) * conc_center +
+           (1 - sy * (alpha_center_center + alpha_center)) * conc_center +
            sy * alpha_center * conc_bc
 end