diff --git a/README.md b/README.md
index 440cc4d..d796148 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@
 [![workflow status](https://github.com/hyparam/hyparquet/actions/workflows/ci.yml/badge.svg)](https://github.com/hyparam/hyparquet/actions)
 [![mit license](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)
 [![dependencies](https://img.shields.io/badge/Dependencies-0-blueviolet)](https://www.npmjs.com/package/hyparquet?activeTab=dependencies)
+![coverage](https://img.shields.io/badge/Coverage-94-darkred)
 
 Dependency free since 2023!
 
diff --git a/package.json b/package.json
index ccca415..6b759de 100644
--- a/package.json
+++ b/package.json
@@ -28,14 +28,14 @@
   },
   "devDependencies": {
     "@types/node": "20.12.7",
-    "@typescript-eslint/eslint-plugin": "7.7.0",
-    "@vitest/coverage-v8": "1.5.0",
+    "@typescript-eslint/eslint-plugin": "7.7.1",
+    "@vitest/coverage-v8": "1.5.2",
     "eslint": "8.57.0",
     "eslint-plugin-import": "2.29.1",
     "eslint-plugin-jsdoc": "48.2.3",
     "http-server": "14.1.1",
     "hysnappy": "0.3.0",
     "typescript": "5.4.5",
-    "vitest": "1.5.0"
+    "vitest": "1.5.2"
   }
 }
diff --git a/src/hyparquet.d.ts b/src/hyparquet.d.ts
index 40ce2ed..c49e68d 100644
--- a/src/hyparquet.d.ts
+++ b/src/hyparquet.d.ts
@@ -1,4 +1,6 @@
-export { AsyncBuffer, FileMetaData, SchemaTree } from './types'
+import type { AsyncBuffer, Compressors, FileMetaData, SchemaTree } from './types.d.ts'
+
+export type { AsyncBuffer, FileMetaData, SchemaTree }
 
 /**
  * Read parquet data rows from a file-like object.
@@ -22,7 +24,7 @@ export { AsyncBuffer, FileMetaData, SchemaTree } from './types'
  * @param {Compressors} [options.compressor] custom decompressors
  * @returns {Promise<void>} resolves when all requested rows and columns are parsed
  */
-export async function parquetRead(options: ParquetReadOptions): Promise<void>
+export function parquetRead(options: ParquetReadOptions): Promise<void>
 
 /**
  * Read parquet metadata from an async buffer.
@@ -48,7 +50,7 @@ export async function parquetRead(options: ParquetReadOptions): Promise<void>
  * @param {number} initialFetchSize initial fetch size in bytes (default 512kb)
  * @returns {Promise<FileMetaData>} parquet metadata object
  */
-export async function parquetMetadataAsync(asyncBuffer: AsyncBuffer, initialFetchSize: number = 1 << 19 /* 512kb */): Promise<FileMetaData>
+export function parquetMetadataAsync(asyncBuffer: AsyncBuffer, initialFetchSize?: number): Promise<FileMetaData>
 
 /**
  * Read parquet metadata from a buffer
diff --git a/src/read.js b/src/read.js
index e64b4e0..856a5e3 100644
--- a/src/read.js
+++ b/src/read.js
@@ -137,13 +137,15 @@ async function readRowGroup(options, rowGroup, groupStart) {
     }
 
     // use pre-loaded row group byte data if available, else read column data
+    /** @type {Promise<ArrayBuffer>} */
     let buffer
     let bufferOffset = 0
     if (groupBuffer) {
       buffer = Promise.resolve(groupBuffer)
       bufferOffset = columnStartByte - groupStartByte
     } else {
-      buffer = file.slice(columnStartByte, columnEndByte)
+      // wrap awaitable to ensure it's a promise
+      buffer = Promise.resolve(file.slice(columnStartByte, columnEndByte))
     }
 
     // read column data async
diff --git a/src/types.d.ts b/src/types.d.ts
index 3f90c40..8ad741c 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -1,9 +1,11 @@
+type Awaitable<T> = T | Promise<T>
+
 /**
  * File-like object that can read slices of a file asynchronously.
  */
 export interface AsyncBuffer {
   byteLength: number
-  slice(start: number, end?: number): Promise<ArrayBuffer>
+  slice(start: number, end?: number): Awaitable<ArrayBuffer>
 }
 
 /**
diff --git a/test/files/README.md b/test/files/README.md
index beb0bcb..e63083b 100644
--- a/test/files/README.md
+++ b/test/files/README.md
@@ -3,5 +3,3 @@
 This directory contains binary test files from [apache/parquet-testing](https://github.com/apache/parquet-testing), under the [Apache 2.0 license](https://www.apache.org/licenses/LICENSE-2.0).
 
 Copyright 2004 The Apache Software Foundation (http://www.apache.org/).
-
-
diff --git a/test/metadata.test.js b/test/metadata.test.js
index 6dd062a..fb5aa5a 100644
--- a/test/metadata.test.js
+++ b/test/metadata.test.js
@@ -63,6 +63,7 @@ describe('parquetMetadataAsync', () => {
 
   it('throws for asyncBuffer undefined', async () => {
     const arrayBuffer = undefined
+    // @ts-expect-error testing invalid input
     await expect(parquetMetadataAsync(arrayBuffer)).rejects
       .toThrow('parquet file is required')
   })
diff --git a/test/read.test.js b/test/read.test.js
index 9644d4a..5357b5e 100644
--- a/test/read.test.js
+++ b/test/read.test.js
@@ -5,13 +5,14 @@ import { fileToAsyncBuffer } from './helpers.js'
 
 describe('parquetRead', () => {
   it('throws error for undefined file', async () => {
-    const file = undefined
-    await expect(parquetRead({ file }))
+    // @ts-expect-error testing invalid input
+    await expect(parquetRead({ file: undefined }))
       .rejects.toThrow('parquet file is required')
   })
 
   it('throws error for undefined byteLength', async () => {
     const file = { byteLength: undefined, slice: () => new ArrayBuffer(0) }
+    // @ts-expect-error testing invalid input
     await expect(parquetRead({ file }))
       .rejects.toThrow('parquet file byteLength is required')
   })
diff --git a/tsconfig.json b/tsconfig.json
index 6465dd1..d4f8118 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,7 +6,7 @@
     "module": "nodenext",
     "noEmit": true,
     "resolveJsonModule": true,
-    "skipLibCheck": true,
+    "skipLibCheck": false,
     "strict": true,
     "target": "esnext",
   },