diff --git a/TileStache/Goodies/VecTiles/oscimap.py b/TileStache/Goodies/VecTiles/oscimap.py
index fb9f585b..c14fed5e 100644
--- a/TileStache/Goodies/VecTiles/oscimap.py
+++ b/TileStache/Goodies/VecTiles/oscimap.py
@@ -21,7 +21,8 @@
 # tiles are padded by this number of pixels for the current zoom level (OSciMap uses this to cover up seams between tiles)
 padding = 5
 
-def encode(file, features, coord, layer_name):
+def encode(file, features, coord, layer_name=''):
+        layer_name = layer_name or ''
         tile = VectorTile(extents)
 
         for feature in features: