diff --git a/book/src/contributing/ast_ebnf.md b/book/src/contributing/ast_ebnf.md
index 83b35619b..f32d94645 100644
--- a/book/src/contributing/ast_ebnf.md
+++ b/book/src/contributing/ast_ebnf.md
@@ -55,7 +55,7 @@ ty ::=
 | (ty "->")* ty
 | impl "::" ident
 | "impl" ty
-| (goal)*
+| "dyn" (goal)*
 ```
 
 The patterns allowed reflect these types. Wildcard patterns, literal