diff --git a/src/equations/equations.jl b/src/equations/equations.jl
index 4c8f7ec0..d003e40a 100644
--- a/src/equations/equations.jl
+++ b/src/equations/equations.jl
@@ -570,7 +570,7 @@ function solve_system_matrix!(dv, system_matrix, rhs,
                                                SerreGreenNaghdiEquations1D},
                               D1, cache, ::BoundaryConditionReflecting)
     scale_by_mass_matrix!(rhs, D1)
-    solve_system_matrix!(dv, system_matrix, (@view rhs[2:(end - 1)]), equations, D1, cache)
+    solve_system_matrix!(dv, system_matrix, (@view rhs[(begin + 1):(end - 1)]), equations, D1, cache)
 end
 
 function solve_system_matrix!(dv, system_matrix, rhs,