diff --git a/src/index.ts b/src/index.ts
index 441a91d1..65cf10d4 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,7 +2,7 @@ import path from 'path'
 import fs from 'fs'
 import { Worker } from 'worker_threads'
 import type { Buildable, MarkRequired } from 'ts-essentials'
-import { removeFiles, debouncePromise, slash } from './utils'
+import { removeFiles, debouncePromise, slash, MaybePromise } from './utils'
 import { loadTsupConfig } from './load'
 import glob from 'globby'
 import { loadTsConfig } from 'bundle-require'
@@ -39,7 +39,7 @@ export const defineConfig = (
     | ((
         /** The options derived from CLI flags */
         overrideOptions: Options
-      ) => Options | Options[])
+      ) => MaybePromise<Options | Options[]>)
 ) => options
 
 const killProcess = ({
@@ -126,7 +126,9 @@ export async function build(_options: Options) {
     _options.config === false ? {} : await loadTsupConfig(process.cwd())
 
   const configData =
-    typeof config.data === 'function' ? config.data(_options) : config.data
+    typeof config.data === 'function'
+      ? await config.data(_options)
+      : config.data
 
   await Promise.all(
     [...(Array.isArray(configData) ? configData : [configData])].map(
diff --git a/src/plugin.ts b/src/plugin.ts
index 8ee0fe6a..ad8f0b95 100644
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -4,6 +4,7 @@ import { SourceMapConsumer, SourceMapGenerator, RawSourceMap } from 'source-map'
 import { Format, NormalizedOptions } from '.'
 import { outputFile } from './fs'
 import { Logger } from './log'
+import { MaybePromise } from './utils'
 
 export type ChunkInfo = {
   type: 'chunk'
@@ -22,8 +23,6 @@ export type AssetInfo = {
   contents: Uint8Array
 }
 
-type MaybePromise<T> = T | Promise<T>
-
 export type RenderChunk = (
   this: PluginContext,
   code: string,
diff --git a/src/utils.ts b/src/utils.ts
index 2fcc94a0..9b9ec271 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -3,6 +3,8 @@ import glob from 'globby'
 import resolveFrom from 'resolve-from'
 import strip from 'strip-json-comments'
 
+export type MaybePromise<T> = T | Promise<T>
+
 export type External =
   | string
   | RegExp