diff --git a/README.md b/README.md
index e74fc75a5..fbb526220 100644
--- a/README.md
+++ b/README.md
@@ -24,10 +24,11 @@ below for explanation of `emit_*` calls):
 
     require 'parser/current'
     # opt-in to most recent AST format:
-    Parser::Builders::Default.emit_lambda   = true
-    Parser::Builders::Default.emit_procarg0 = true
-    Parser::Builders::Default.emit_encoding = true
-    Parser::Builders::Default.emit_index    = true
+    Parser::Builders::Default.emit_lambda              = true
+    Parser::Builders::Default.emit_procarg0            = true
+    Parser::Builders::Default.emit_encoding            = true
+    Parser::Builders::Default.emit_index               = true
+    Parser::Builders::Default.emit_arg_inside_procarg0 = true
 
 Parse a chunk of code: