diff --git a/js/index.ts b/js/index.ts
index cf2f7c0..057b7c5 100644
--- a/js/index.ts
+++ b/js/index.ts
@@ -141,7 +141,15 @@ export enum Compression {
 	Zstd = 4,
 }
 
-async function tryDecompress(buf: ArrayBuffer, compression: Compression) {
+type DecompressFunc = (
+	buf: ArrayBuffer,
+	compression: Compression
+) => Promise<ArrayBuffer>;
+
+async function fflateDecompress(
+	buf: ArrayBuffer,
+	compression: Compression
+): Promise<ArrayBuffer> {
 	if (compression === Compression.None || compression === Compression.Unknown) {
 		return buf;
 	} else if (compression === Compression.Gzip) {
@@ -416,6 +424,7 @@ export interface Cache {
 
 async function getHeaderAndRoot(
 	source: Source,
+	decompress: DecompressFunc,
 	prefetch: boolean,
 	current_etag?: string
 ): Promise<[Header, [string, number, Entry[] | ArrayBuffer]?]> {
@@ -461,7 +470,7 @@ async function getHeaderAndRoot(
 			header.rootDirectoryLength;
 
 		const rootDir = deserializeIndex(
-			await tryDecompress(rootDirData, header.internalCompression)
+			await decompress(rootDirData, header.internalCompression)
 		);
 		return [header, [dirKey, ENTRY_SIZE_BYTES * rootDir.length, rootDir]];
 	}
@@ -471,6 +480,7 @@ async function getHeaderAndRoot(
 
 async function getDirectory(
 	source: Source,
+	decompress: DecompressFunc,
 	offset: number,
 	length: number,
 	header: Header
@@ -481,7 +491,7 @@ async function getDirectory(
 		throw new EtagMismatch(resp.etag);
 	}
 
-	const data = await tryDecompress(resp.data, header.internalCompression);
+	const data = await decompress(resp.data, header.internalCompression);
 	const directory = deserializeIndex(data);
 	if (directory.length === 0) {
 		throw new Error("Empty directory is invalid");
@@ -502,13 +512,19 @@ export class ResolvedValueCache {
 	maxSizeBytes: number;
 	counter: number;
 	prefetch: boolean;
+	decompress: DecompressFunc;
 
-	constructor(maxSizeBytes = 64000000, prefetch = true) {
+	constructor(
+		maxSizeBytes = 64000000,
+		prefetch = true,
+		decompress: DecompressFunc = fflateDecompress
+	) {
 		this.cache = new Map<string, ResolvedValue>();
 		this.sizeBytes = 0;
 		this.maxSizeBytes = maxSizeBytes;
 		this.counter = 1;
 		this.prefetch = prefetch;
+		this.decompress = decompress;
 	}
 
 	async getHeader(source: Source, current_etag?: string): Promise<Header> {
@@ -519,7 +535,12 @@ export class ResolvedValueCache {
 			return data as Header;
 		}
 
-		const res = await getHeaderAndRoot(source, this.prefetch, current_etag);
+		const res = await getHeaderAndRoot(
+			source,
+			this.decompress,
+			this.prefetch,
+			current_etag
+		);
 		if (res[1]) {
 			this.cache.set(res[1][0], {
 				lastUsed: this.counter++,
@@ -552,7 +573,13 @@ export class ResolvedValueCache {
 			return data as Entry[];
 		}
 
-		const directory = await getDirectory(source, offset, length, header);
+		const directory = await getDirectory(
+			source,
+			this.decompress,
+			offset,
+			length,
+			header
+		);
 		this.cache.set(cacheKey, {
 			lastUsed: this.counter++,
 			data: directory,
@@ -631,13 +658,19 @@ export class SharedPromiseCache {
 	maxSizeBytes: number;
 	counter: number;
 	prefetch: boolean;
+	decompress: DecompressFunc;
 
-	constructor(maxSizeBytes = 64000000, prefetch = true) {
+	constructor(
+		maxSizeBytes = 64000000,
+		prefetch = true,
+		decompress: DecompressFunc = fflateDecompress
+	) {
 		this.cache = new Map<string, SharedPromiseCacheValue>();
 		this.sizeBytes = 0;
 		this.maxSizeBytes = maxSizeBytes;
 		this.counter = 1;
 		this.prefetch = prefetch;
+		this.decompress = decompress;
 	}
 
 	async getHeader(source: Source, current_etag?: string): Promise<Header> {
@@ -649,7 +682,7 @@ export class SharedPromiseCache {
 		}
 
 		const p = new Promise<Header>((resolve, reject) => {
-			getHeaderAndRoot(source, this.prefetch, current_etag)
+			getHeaderAndRoot(source, this.decompress, this.prefetch, current_etag)
 				.then((res) => {
 					if (this.cache.has(cacheKey)) {
 						this.cache.get(cacheKey)!.size = HEADER_SIZE_BYTES;
@@ -688,7 +721,7 @@ export class SharedPromiseCache {
 		}
 
 		const p = new Promise<Entry[]>((resolve, reject) => {
-			getDirectory(source, offset, length, header)
+			getDirectory(source, this.decompress, offset, length, header)
 				.then((directory) => {
 					resolve(directory);
 					if (this.cache.has(cacheKey)) {
@@ -771,13 +804,23 @@ export class SharedPromiseCache {
 export class PMTiles {
 	source: Source;
 	cache: Cache;
+	decompress: DecompressFunc;
 
-	constructor(source: Source | string, cache?: Cache) {
+	constructor(
+		source: Source | string,
+		cache?: Cache,
+		decompress?: DecompressFunc
+	) {
 		if (typeof source === "string") {
 			this.source = new FetchSource(source);
 		} else {
 			this.source = source;
 		}
+		if (decompress) {
+			this.decompress = decompress;
+		} else {
+			this.decompress = fflateDecompress;
+		}
 		if (cache) {
 			this.cache = cache;
 		} else {
@@ -843,7 +886,7 @@ export class PMTiles {
 						throw new EtagMismatch(resp.etag);
 					}
 					return {
-						data: await tryDecompress(resp.data, header.tileCompression),
+						data: await this.decompress(resp.data, header.tileCompression),
 						cacheControl: resp.cacheControl,
 						expires: resp.expires,
 					};
@@ -886,7 +929,10 @@ export class PMTiles {
 		if (header.etag && header.etag !== resp.etag) {
 			throw new EtagMismatch(resp.etag);
 		}
-		const decompressed = await tryDecompress(resp.data, header.internalCompression);
+		const decompressed = await this.decompress(
+			resp.data,
+			header.internalCompression
+		);
 		const dec = new TextDecoder("utf-8");
 		return JSON.parse(dec.decode(decompressed));
 	}