diff --git a/blocks/file-blocks/markdown-edit/extensions.ts b/blocks/file-blocks/markdown-edit/extensions.ts
index afad1b5..4798068 100644
--- a/blocks/file-blocks/markdown-edit/extensions.ts
+++ b/blocks/file-blocks/markdown-edit/extensions.ts
@@ -168,6 +168,7 @@ export function makeExtensions({
                   return -1;
                 const hasIncludedLink = match[0].indexOf("](http") !== -1;
                 if (hasIncludedLink) return -1;
+                if (!firstMatch) return -1;
                 return cx.addElement(
                   cx.elt("URL", start, start + 1 + firstMatch.length)
                 );