diff --git a/packages/babel-parser/src/parser/base.js b/packages/babel-parser/src/parser/base.js
index f4fb9f3b66e0..fc4f9e33b1d9 100644
--- a/packages/babel-parser/src/parser/base.js
+++ b/packages/babel-parser/src/parser/base.js
@@ -4,12 +4,14 @@ import type { Options } from "../options";
 import type State from "../tokenizer/state";
 import type { PluginsMap } from "./index";
 import type ScopeHandler from "../util/scope";
+import type ProductionParameterHandler from "../util/production-parameter";
 
 export default class BaseParser {
   // Properties set by constructor in index.js
   options: Options;
   inModule: boolean;
   scope: ScopeHandler<*>;
+  param: ProductionParameterHandler;
   plugins: PluginsMap;
   filename: ?string;
   sawUnambiguousESM: boolean = false;