diff --git a/packages/babel-generator/src/index.js b/packages/babel-generator/src/index.js
index 32a1cbec02..2c0a50c016 100644
--- a/packages/babel-generator/src/index.js
+++ b/packages/babel-generator/src/index.js
@@ -34,7 +34,7 @@ export class CodeGenerator extends Printer {
   }
 
   format: {
-    shouldPrintComment: boolean;
+    shouldPrintComment: (comment: string) => boolean;
     retainLines: boolean;
     comments: boolean;
     auxiliaryCommentBefore: string;