diff --git a/src/cases/wave_reader_side/wave_reader_side.cpp b/src/cases/wave_reader_side/wave_reader_side.cpp
index 9250104a6034268c464aa4fd635406137e4c7a71..72b0b0e1875aead43e901f2ea6aa4bcec4d69ddc 100644
--- a/src/cases/wave_reader_side/wave_reader_side.cpp
+++ b/src/cases/wave_reader_side/wave_reader_side.cpp
@@ -596,8 +596,8 @@ class userControl : public BaseCase {
                 // the config file is the physical extent we're considering the boundary
                 // layer, so mask out this region.  
                 double dz = Lz/Nz;
-                *boundary_mask = 1 - 0.25*( (1 + tanh( ((MinZ + Lz - bl_width) - (*zgrid)(ii,jj,kk))/(0.25*bl_width)))) * // flat wall boundary
-                                        (1 + tanh( ((*zgrid)(ii,jj,kk) - (MinZ + bl_width + topo(ii)))/(0.25*bl_width))); // Bumpy wall boundary
+                *boundary_mask = 0.25*( (1 + tanh( ((MinZ + Lz - bl_width) - (*zgrid)(ii,jj,kk))/(0.25*bl_width)))) * // flat wall boundary
+                                      (1 + tanh( ((*zgrid)(ii,jj,kk) - (MinZ + bl_width + topo(ii)))/(0.25*bl_width))); // Bumpy wall boundary
                 Array<double,1> const & qz = *get_quad_z(); // Keep reference to z-quadrature weights
                 for (int i = boundary_mask_2d->lbound(firstDim); i <= boundary_mask_2d->ubound(firstDim); i++) {
                     for (int k = boundary_mask_2d->lbound(thirdDim); k <= boundary_mask_2d->ubound(thirdDim); k++) {