diff --git a/miniwalker.go b/miniwalker.go
index 5aaf623..71b5414 100644
--- a/miniwalker.go
+++ b/miniwalker.go
@@ -34,6 +34,8 @@ func (mw *miniWalker) LeaveChildNode(key string, w walker.Walkable) {}
 func (mw *miniWalker) EnterChildList(key string, w walker.Walkable) {}
 func (mw *miniWalker) LeaveChildList(key string, w walker.Walkable) {}
 
+var _ walker.Visitor = &miniWalker{} // interface assertion
+
 func walk(n node.Node, cb func(node.Node) error) error {
 	mw := miniWalker{cb: cb}
 	n.Walk(&mw)