diff --git a/cameo/poly2d.c b/cameo/poly2d.c
index a8d1460..d738e66 100644
--- a/cameo/poly2d.c
+++ b/cameo/poly2d.c
@@ -1,8 +1,8 @@
 /*
  * poly2d.c - Poly2D interface functions
  *
- * Written 2012 by Werner Almesberger
- * Copyright 2012 Werner Almesberger
+ * Written 2012, 2015 by Werner Almesberger
+ * Copyright 2012, 2015 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdlib.h>
 #include <math.h>
 #include <assert.h>
 
@@ -46,6 +47,8 @@ struct p2d *paths_to_polys_z(const struct path *paths,
 		if (path->first->z < zmin || path->first->z > zmax)
 			continue;
 		*last = path_to_poly(path);
+		if (!*last)
+			continue;
 		last = &(*last)->next;
 	}
 	return polys;