diff --git a/src/pybind11 b/src/pybind11
index 2d59b43c..a8b3ff30 160000
--- a/src/pybind11
+++ b/src/pybind11
@@ -1 +1 @@
-Subproject commit 2d59b43cbf8793119fb92726ce8eb33441469e3e
+Subproject commit a8b3ff30f9649459021adc80f98a945d3ac675a5
diff --git a/utils/mcxpreview.m b/utils/mcxpreview.m
index 3dd8a8cf..aaacec04 100644
--- a/utils/mcxpreview.m
+++ b/utils/mcxpreview.m
@@ -68,6 +68,10 @@
     if(isfield(cfg(i),'vol') && ~isfield(cfg(i),'node'))
         % render mcxlab voxelated domain
         dim=size(cfg(i).vol);
+        if(ndims(cfg(i).vol)==4) % for spatially varying medium
+            dim=dim(2:end);
+            cfg(i).vol=ones(dim);
+        end
         [bbxno,bbxfc]=latticegrid(0:dim(1):dim(1),0:dim(2):dim(2),0:dim(3):dim(3));
         hbbx=plotmesh((bbxno+offset)*voxelsize,bbxfc,'facecolor','none');