diff --git a/overviewer_core/src/primitives/overlay-mineral.c b/overviewer_core/src/primitives/overlay-mineral.c
index 5d6f22e..b658433 100644
--- a/overviewer_core/src/primitives/overlay-mineral.c
+++ b/overviewer_core/src/primitives/overlay-mineral.c
@@ -90,6 +90,7 @@ overlay_mineral_start(void *data, RenderState *state, PyObject *support) {
     /* now do custom initializations */
     self = (RenderPrimitiveMineral *)data;
     
+    // opt is a borrowed reference.  do not deref 
     if (!render_mode_parse_option(support, "minerals", "O", &(opt)))
         return 1;
     if (opt && opt != Py_None) {
@@ -119,7 +120,6 @@ overlay_mineral_start(void *data, RenderState *state, PyObject *support) {
     } else {
         self->minerals = default_minerals;
     }
-    Py_XDECREF(opt);
     
     /* setup custom color */
     self->parent.get_color = get_color;
diff --git a/overviewer_core/tileset.py b/overviewer_core/tileset.py
index a2a8f0a..6919884 100644
--- a/overviewer_core/tileset.py
+++ b/overviewer_core/tileset.py
@@ -508,7 +508,7 @@ class TileSet(object):
         """
         def bgcolorformat(color):
             return "#%02x%02x%02x" % color[0:3]
-        isOverlay = True in [True for x in self.options.get("rendermode") if isinstance(x, rendermodes.Overlay)]
+        isOverlay = not any(isinstance(x, rendermodes.Base) for x in self.options.get("rendermode"))
         
         d = dict(name = self.options.get('title'),
                 zoomLevels = self.treedepth,