diff --git a/packages/babel-parser/src/plugins/typescript/index.js b/packages/babel-parser/src/plugins/typescript/index.js
index e35d75709dd3..9fe99cbff213 100644
--- a/packages/babel-parser/src/plugins/typescript/index.js
+++ b/packages/babel-parser/src/plugins/typescript/index.js
@@ -2274,7 +2274,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       leftStartLoc: Position,
       minPrec: number,
     ) {
-      let isSatisfies: boolean;
+      let isSatisfies: ?boolean;
       if (
         tokenOperatorPrecedence(tt._in) > minPrec &&
         !this.hasPrecedingLineBreak() &&