diff --git a/api/nlopt.c b/api/nlopt.c
index f29e4ca87574965d4f80a40719dba923bcb97de2..e13980e4d3d8f08c5233a0b13c29c2103ed30c96 100644
--- a/api/nlopt.c
+++ b/api/nlopt.c
@@ -194,6 +194,10 @@ static nlopt_result nlopt_minimize_(
      nlopt_data d;
      nlopt_stopping stop;
 
+     /* some basic argument checks */
+     if (n <= 0 || !f || !lb || !ub || !x || !fmin)
+	  return NLOPT_INVALID_ARGS;
+
      d.f = f;
      d.f_data = f_data;
      d.lb = lb;
diff --git a/cdirect/cdirect.c b/cdirect/cdirect.c
index f910de1f6eaf44c6780a7dfcb8b5546fa505b7fe..2684cc72c40d80dc7b3a08eda46874ea62d21518 100644
--- a/cdirect/cdirect.c
+++ b/cdirect/cdirect.c
@@ -19,9 +19,10 @@
  * measure (d) of the rectangle, [2..n+1] are the coordinates of the
  * center (c), and [n+2..2n+1] are the widths of the sides (w).
  *
- * a list of rectangles is just an array of N hyper-rectangles
- * stored as an N x L in row-major order.  Generally,
- * we allocate more than we need, allocating Na hyper-rectangles.
+ * we store the hyper-rectangles in a red-black tree, sorted by (d,f)
+ * in lexographic order, to allow us to perform quick convex-hull
+ * calculations (in the future, we might make this data structure
+ * more sophisticated based on the dynamic convex-hull literature).
  *
  * n > 0 always
  */