diff --git a/overviewer_core/tileset.py b/overviewer_core/tileset.py
index 1a91f51..bae0a52 100644
--- a/overviewer_core/tileset.py
+++ b/overviewer_core/tileset.py
@@ -513,7 +513,7 @@ class TileSet(object):
         """
         def bgcolorformat(color):
             return "#%02x%02x%02x" % color[0:3]
-        isOverlay = not any(isinstance(x, rendermodes.Base) for x in self.options.get("rendermode"))
+        isOverlay = ("overlay" in self.options) or (not any(isinstance(x, rendermodes.Base) for x in self.options.get("rendermode")))
         
         d = dict(name = self.options.get('title'),
                 zoomLevels = self.treedepth,