diff --git a/lib/rbtree.c b/lib/rbtree.c
index 1e55ba1..48499c2 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -322,6 +322,9 @@
 {
 	struct rb_node *parent;
 
+	if (rb_parent(node) == node)
+		return NULL;
+
 	/* If we have a right-hand child, go down and then left as far
 	   as we can. */
 	if (node->rb_right) {
@@ -348,6 +351,9 @@
 {
 	struct rb_node *parent;
 
+	if (rb_parent(node) == node)
+		return NULL;
+
 	/* If we have a left-hand child, go down and then right as far
 	   as we can. */
 	if (node->rb_left) {