diff --git a/matlab/AddMSLPort.m b/matlab/AddMSLPort.m
index 1bec8eb..8880a0f 100644
--- a/matlab/AddMSLPort.m
+++ b/matlab/AddMSLPort.m
@@ -97,8 +97,8 @@ v3_stop(idx_prop)    = meshlines(3);
 idx = interp1( mesh{idx_width}, 1:numel(mesh{idx_width}), nstart(idx_width), 'nearest' );
 i1_start(idx_width)  = mesh{idx_width}(idx) - diff(mesh{idx_width}(idx-1:idx))/2;
 idx = interp1( mesh{idx_height}, 1:numel(mesh{idx_height}), start(idx_height), 'nearest' );
-i1_start(idx_height) = mesh{idx_height}(idx) - diff(mesh{idx_height}(idx-1:idx))/2;
-i1_stop(idx_height)  = mesh{idx_height}(idx) + diff(mesh{idx_height}(idx:idx+1))/2;
+i1_start(idx_height) = mesh{idx_height}(idx-1) - diff(mesh{idx_height}(idx-2:idx-1))/2;
+i1_stop(idx_height)  = mesh{idx_height}(idx+1) + diff(mesh{idx_height}(idx+1:idx+2))/2;
 i1_start(idx_prop)   = sum(meshlines(1:2))/2;
 i1_stop(idx_prop)    = i1_start(idx_prop);
 idx = interp1( mesh{idx_width}, 1:numel(mesh{idx_width}), nstop(idx_width), 'nearest' );