diff --git a/iterator.go b/iterator.go
index a509ed1..2aaa62f 100644
--- a/iterator.go
+++ b/iterator.go
@@ -6,6 +6,7 @@ package iavl
 import (
 	"bytes"
 	"errors"
+	"fmt"
 
 	dbm "github.com/tendermint/tm-db"
 )
@@ -76,19 +77,19 @@ func (nodes *delayedNodes) length() int {
 // 1. If it is not an delayed node (node.delayed == false) it immediately returns it.
 //
 // A. If the `node` is a branch node:
-// 1. If the traversal is postorder, then append the current node to the t.delayedNodes,
-//    with `delayed` set to false. This makes the current node returned *after* all the children
-//    are traversed, without being expanded.
-// 2. Append the traversable children nodes into the `delayedNodes`, with `delayed` set to true. This
-//    makes the children nodes to be traversed, and expanded with their respective children.
-// 3. If the traversal is preorder, (with the children to be traversed already pushed to the
-//    `delayedNodes`), returns the current node.
-// 4. Call `traversal.next()` to further traverse through the `delayedNodes`.
+//  1. If the traversal is postorder, then append the current node to the t.delayedNodes,
+//     with `delayed` set to false. This makes the current node returned *after* all the children
+//     are traversed, without being expanded.
+//  2. Append the traversable children nodes into the `delayedNodes`, with `delayed` set to true. This
+//     makes the children nodes to be traversed, and expanded with their respective children.
+//  3. If the traversal is preorder, (with the children to be traversed already pushed to the
+//     `delayedNodes`), returns the current node.
+//  4. Call `traversal.next()` to further traverse through the `delayedNodes`.
 //
 // B. If the `node` is a leaf node, it will be returned without expand, by the following process:
-// 1. If the traversal is postorder, the current node will be append to the `delayedNodes` with `delayed`
-//    set to false, and immediately returned at the subsequent call of `traversal.next()` at the last line.
-// 2. If the traversal is preorder, the current node will be returned.
+//  1. If the traversal is postorder, the current node will be append to the `delayedNodes` with `delayed`
+//     set to false, and immediately returned at the subsequent call of `traversal.next()` at the last line.
+//  2. If the traversal is preorder, the current node will be returned.
 func (t *traversal) next() (*Node, error) {
 	// End of traversal.
 	if t.delayedNodes.length() == 0 {
@@ -230,6 +231,9 @@ func (iter *Iterator) Next() {
 	node, err := iter.t.next()
 	// TODO: double-check if this error is correctly handled.
 	if node == nil || err != nil {
+		if err != nil {
+			fmt.Printf("iterator closed due to %s\n", err)
+		}
 		iter.t = nil
 		iter.valid = false
 		return