diff --git a/doc/AST_FORMAT.md b/doc/AST_FORMAT.md
index 16f52f4d4..b53f582e2 100644
--- a/doc/AST_FORMAT.md
+++ b/doc/AST_FORMAT.md
@@ -1145,6 +1145,17 @@ Format:
  ~~~~~ expression
 ~~~
 
+### Block nil argument (Prism only)
+
+Format:
+
+~~~
+(blocknilarg)
+"&nil"
+  ~~~ name
+ ~~~~ expression
+~~~
+
 ### Objective-C arguments
 
 MacRuby includes a few more syntactic "arguments" whose name becomes
diff --git a/lib/parser/meta.rb b/lib/parser/meta.rb
index fcbaff167..b7ed0ece2 100644
--- a/lib/parser/meta.rb
+++ b/lib/parser/meta.rb
@@ -7,7 +7,7 @@ module Meta
     # These are node types required by `Prism::Translation::Parser`, 
     # which has advanced syntax support ahead of the Parser gem.
     PRISM_TRANSLATION_PARSER_NODE_TYPES = %i(
-      itarg itblock
+      itarg itblock blocknilarg
     ).freeze
     private_constant :PRISM_TRANSLATION_PARSER_NODE_TYPES