diff --git a/prep_toposm_data b/prep_toposm_data
index 8394291..ef6090e 100755
--- a/prep_toposm_data
+++ b/prep_toposm_data
@@ -95,12 +95,11 @@ for y in `seq $BOTTOM $TOP`; do
 done; done
 
 # generate overviews and VRT layers
-pushd . ; cd $HILLSHADE_DIR
-gdalbuildvrt -overwrite all.vrt *.tif
-popd
-pushd . ; cd $HYPSORELIEF_DIR
-gdalbuildvrt -vrtnodata "128 128 128" -overwrite all.vrt *.tif
-popd
+for d in $HILLSHADE_DIR $HYPSORELIEF_DIR ; do
+    pushd . ; cd $d
+    gdalbuildvrt all.vrt *.tif
+    popd
+done
 
 # reproject NLCD data, add overviews, and copy VRT file (with
 # the custom color table).