diff --git a/packages/gatsby/src/utils/app-data.ts b/packages/gatsby/src/utils/app-data.ts
index 311d84cf8bc8f..0b3f0b9610ef0 100644
--- a/packages/gatsby/src/utils/app-data.ts
+++ b/packages/gatsby/src/utils/app-data.ts
@@ -3,11 +3,10 @@ import path from "path"
 
 const APP_DATA_JSON = `app-data.json`
 
-export const write = (publicDir: string, hash: string): void => {
+export const write = (publicDir: string, hash: string): Promise<void> =>
   fs.outputJson(path.join(publicDir, `page-data`, APP_DATA_JSON), {
     webpackCompilationHash: hash,
   })
-}
 
 export const exists = (publicDir: string): boolean =>
   fs.pathExistsSync(path.join(publicDir, `page-data`, APP_DATA_JSON))