diff --git a/src/to_markdown.js b/src/to_markdown.js
index <HASH>..<HASH> 100644
--- a/src/to_markdown.js
+++ b/src/to_markdown.js
@@ -237,6 +237,7 @@ export class MarkdownSerializerState {
   // Render the given node as a block.
   render(node, parent, index) {
     if (typeof parent == "number") throw new Error("!")
+    if (!this.nodes[node.type.name]) throw new Error("Token type `" + node.type.name + "` not supported by Markdown renderer")
     this.nodes[node.type.name](this, node, parent, index)
   }
Add renderering error if renderer is not defined

This helps with debugging new renderers.