diff --git a/package.json b/package.json
index bdb44fa..47442f8 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,6 @@
   "repository": "github:DerekNonGeneric/proposal-assertion-error",
   "license": "MIT",
   "devDependencies": {
-    "ecmarkup": "16.0.0"
+    "ecmarkup": "21.5.0"
   }
 }