diff --git a/clang/lib/Tooling/Syntax/Pseudo/cxx.bnf b/clang/lib/Tooling/Syntax/Pseudo/cxx.bnf
--- a/clang/lib/Tooling/Syntax/Pseudo/cxx.bnf
+++ b/clang/lib/Tooling/Syntax/Pseudo/cxx.bnf
@@ -69,7 +69,7 @@
 lambda-expression := lambda-introducer lambda-declarator_opt compound-statement
 lambda-expression := lambda-introducer < template-parameter-list > requires-clause_opt lambda-declarator_opt compound-statement
 lambda-introducer := [ lambda-capture_opt ]
-lambda-declarator := ( parameter-declaration-clause ) decl-specifier-seq_opt noexcept-specifier_opt trailing-return-type_opt requires-clause_opt
+lambda-declarator := ( parameter-declaration-clause_opt ) decl-specifier-seq_opt noexcept-specifier_opt trailing-return-type_opt requires-clause_opt
 lambda-capture := capture-default
 lambda-capture := capture-list
 lambda-capture := capture-default , capture-list