diff --git a/packages/gatsby/src/bootstrap/index.js b/packages/gatsby/src/bootstrap/index.js
index 9b8574ed208dc..4f6dd5eaa16d4 100644
--- a/packages/gatsby/src/bootstrap/index.js
+++ b/packages/gatsby/src/bootstrap/index.js
@@ -20,7 +20,7 @@ const loadThemes = require(`./load-themes`)
 const report = require(`gatsby-cli/lib/reporter`)
 import { getConfigFile } from "./get-config-file"
 const tracer = require(`opentracing`).globalTracer()
-const preferDefault = require(`./prefer-default`)
+import { preferDefault } from "./prefer-default"
 import { removeStaleJobs } from "./remove-stale-jobs"
 
 // Show stack trace on unhandled promises.
diff --git a/packages/gatsby/src/bootstrap/load-themes/index.js b/packages/gatsby/src/bootstrap/load-themes/index.js
index 3ce77bd406896..94e909e6e6ee3 100644
--- a/packages/gatsby/src/bootstrap/load-themes/index.js
+++ b/packages/gatsby/src/bootstrap/load-themes/index.js
@@ -3,7 +3,7 @@ const mergeGatsbyConfig = require(`../../utils/merge-gatsby-config`)
 const Promise = require(`bluebird`)
 const _ = require(`lodash`)
 const debug = require(`debug`)(`gatsby:load-themes`)
-const preferDefault = require(`../prefer-default`)
+import { preferDefault } from "../prefer-default"
 import { getConfigFile } from "../get-config-file"
 const { resolvePlugin } = require(`../load-plugins/load`)
 const reporter = require(`gatsby-cli/lib/reporter`)
diff --git a/packages/gatsby/src/bootstrap/prefer-default.js b/packages/gatsby/src/bootstrap/prefer-default.js
deleted file mode 100644
index 13b0f0fcede97..0000000000000
--- a/packages/gatsby/src/bootstrap/prefer-default.js
+++ /dev/null
@@ -1 +0,0 @@
-module.exports = m => (m && m.default) || m
diff --git a/packages/gatsby/src/bootstrap/prefer-default.ts b/packages/gatsby/src/bootstrap/prefer-default.ts
new file mode 100644
index 0000000000000..603441436b008
--- /dev/null
+++ b/packages/gatsby/src/bootstrap/prefer-default.ts
@@ -0,0 +1 @@
+export const preferDefault = (m: any): any => (m && m.default) || m
diff --git a/packages/gatsby/src/commands/serve.ts b/packages/gatsby/src/commands/serve.ts
index 9189c6fe9a4c9..76b8f76e840b6 100644
--- a/packages/gatsby/src/commands/serve.ts
+++ b/packages/gatsby/src/commands/serve.ts
@@ -12,7 +12,7 @@ import telemetry from "gatsby-telemetry"
 
 import { detectPortInUseAndPrompt } from "../utils/detect-port-in-use-and-prompt"
 import { getConfigFile } from "../bootstrap/get-config-file"
-import preferDefault from "../bootstrap/prefer-default"
+import { preferDefault } from "../bootstrap/prefer-default"
 import { IProgram } from "./types"
 
 interface IMatchPath {