diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7cbdada..b32efae 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -389,8 +389,7 @@
 	struct radix_tree_node *slot;
 
 	height = root->height;
-	if (index > radix_tree_maxindex(height))
-		return NULL;
+	BUG_ON(index > radix_tree_maxindex(height));
 
 	slot = root->rnode;
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;