diff --git a/README.md b/README.md
index 6767a1c..7551093 100644
--- a/README.md
+++ b/README.md
@@ -245,7 +245,7 @@ sdpTransform.grammar['a'].push({
   name: 'xCustomTag',
   reg: /^x-custom-tag:(\d*)/,
   names: ['tagId'],
-  format: 'x-custom:%d
+  format: 'x-custom-tag:%d
 })
 ```