diff --git a/package-lock.json b/package-lock.json
index 67a1fdb..526db32 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "zarr",
-  "version": "0.4.1",
+  "version": "0.4.2",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index cc897d5..7fed878 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "zarr",
-  "version": "0.4.1",
+  "version": "0.4.2",
   "description": "Javascript implementation of Zarr",
   "keywords": [
     "ndarray",
diff --git a/src/core/index.ts b/src/core/index.ts
index ecac027..4cabedc 100644
--- a/src/core/index.ts
+++ b/src/core/index.ts
@@ -11,7 +11,7 @@ import { BasicIndexer, isContiguousSelection, normalizeIntegerSelection } from '
 import { NestedArray } from "../nestedArray";
 import { RawArray } from "../rawArray";
 import { TypedArray, DTYPE_TYPEDARRAY_MAPPING } from '../nestedArray/types';
-import { ValueError, PermissionError, KeyError, BoundsCheckError, ContainsGroupError } from '../errors';
+import { ValueError, PermissionError, BoundsCheckError, ContainsGroupError, isKeyError } from '../errors';
 import { getCodec } from "../compression/registry";
 
 
@@ -35,7 +35,7 @@ export interface SetOptions {
 }
 
 export interface GetRawChunkOptions<O> {
-  storeOptions: O,
+  storeOptions: O;
 }
 
 export class ZarrArray {
@@ -419,7 +419,7 @@ export class ZarrArray {
       }
 
     } catch (error) {
-      if (error instanceof KeyError) {
+      if (isKeyError(error)) {
         // fill with scalar if cKey doesn't exist in store
         if (this.fillValue !== null) {
           out.set(outSelection, this.fillValue);
@@ -448,7 +448,7 @@ export class ZarrArray {
       }
     }
     const cKey = this.chunkKey(chunkCoords);
-    const cdata = this.chunkStore.getItem(cKey, opts?.storeOptions)
+    const cdata = this.chunkStore.getItem(cKey, opts?.storeOptions);
     const buffer = await this.decodeChunk(await cdata);
     const outShape = this.chunks.filter(d => d !== 1); // squeeze chunk dim if 1
     return new RawArray(buffer, outShape, this.dtype);
@@ -502,7 +502,7 @@ export class ZarrArray {
       const cdata = await this.chunkStore.getItem(cKey);
       return new RawArray(await this.decodeChunk(cdata), outShape, this.dtype);
     } catch (error) {
-      if (error instanceof KeyError) {
+      if (isKeyError(error)) {
         // fill with scalar if item doesn't exist
         const data = new DTYPE_TYPEDARRAY_MAPPING[this.dtype](outSize);
         return new RawArray(data.fill(this.fillValue as number), outShape);
@@ -648,14 +648,13 @@ export class ZarrArray {
         const dBytes = await this.decodeChunk(chunkStoreData);
         chunkData = this.toTypedArray(dBytes);
       } catch (error) {
-        if (error instanceof KeyError) {
+        if (isKeyError(error)) {
           // Chunk is not initialized
           chunkData = new dtypeConstr(chunkSize);
           if (this.fillValue !== null) {
             chunkData.fill(this.fillValue);
           }
-        }
-        else {
+        } else {
           // Different type of error - rethrow
           throw error;
         }
diff --git a/src/errors.ts b/src/errors.ts
index bcf40c4..db509a7 100644
--- a/src/errors.ts
+++ b/src/errors.ts
@@ -1,94 +1,118 @@
+export interface ZarrError {
+    __zarr__: string;
+}
+
+function isZarrError(err: unknown): err is ZarrError {
+    return typeof err === 'object' && err !== null && '__zarr__' in err;
+}
+
+export function isKeyError(o: unknown) {
+    return isZarrError(o) && o.__zarr__ === 'KeyError';
+}
+
 // Custom error messages, note we have to patch the prototype of the
 // errors to fix `instanceof` calls, see:
 // https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#extending-built-ins-like-error-array-and-map-may-no-longer-work
-
-export class ContainsArrayError extends Error {
+export class ContainsArrayError extends Error implements ZarrError {
+    __zarr__ = 'ContainsArrayError';
     constructor(path: string) {
         super(`path ${path} contains an array`);
         Object.setPrototypeOf(this, ContainsArrayError.prototype);
     }
 }
 
-export class ContainsGroupError extends Error {
+export class ContainsGroupError extends Error implements ZarrError {
+    __zarr__ = 'ContainsGroupError';
     constructor(path: string) {
         super(`path ${path} contains a group`);
         Object.setPrototypeOf(this, ContainsGroupError.prototype);
     }
 }
 
-export class ArrayNotFoundError extends Error {
+export class ArrayNotFoundError extends Error implements ZarrError {
+    __zarr__ = 'ArrayNotFoundError';
     constructor(path: string) {
         super(`array not found at path ${path}`);
         Object.setPrototypeOf(this, ArrayNotFoundError.prototype);
     }
 }
 
-export class GroupNotFoundError extends Error {
+export class GroupNotFoundError extends Error implements ZarrError {
+    __zarr__ = 'GroupNotFoundError';
     constructor(path: string) {
         super(`ground not found at path ${path}`);
         Object.setPrototypeOf(this, GroupNotFoundError.prototype);
     }
 }
 
-export class PathNotFoundError extends Error {
+export class PathNotFoundError extends Error implements ZarrError {
+    __zarr__ = 'PathNotFoundError';
     constructor(path: string) {
         super(`nothing not found at path ${path}`);
         Object.setPrototypeOf(this, PathNotFoundError.prototype);
     }
 }
 
-export class PermissionError extends Error {
+export class PermissionError extends Error implements ZarrError {
+    __zarr__ = 'PermissionError';
     constructor(message: string) {
         super(message);
         Object.setPrototypeOf(this, PermissionError.prototype);
     }
 }
 
-export class KeyError extends Error {
+export class KeyError extends Error implements ZarrError {
+    __zarr__ = 'KeyError';
     constructor(key: string) {
         super(`key ${key} not present`);
         Object.setPrototypeOf(this, KeyError.prototype);
     }
 }
 
-export class TooManyIndicesError extends RangeError {
+export class TooManyIndicesError extends RangeError implements ZarrError {
+    __zarr__ = 'TooManyIndicesError';
     constructor(selection: any[], shape: number[]) {
         super(`too many indices for array; expected ${shape.length}, got ${selection.length}`);
         Object.setPrototypeOf(this, TooManyIndicesError.prototype);
     }
 }
 
-export class BoundsCheckError extends RangeError {
+export class BoundsCheckError extends RangeError implements ZarrError {
+    __zarr__ = 'BoundsCheckError';
     constructor(message: string) {
         super(message);
         Object.setPrototypeOf(this, BoundsCheckError.prototype);
     }
 }
 
-export class InvalidSliceError extends RangeError {
+export class InvalidSliceError extends RangeError implements ZarrError {
+    __zarr__ = 'InvalidSliceError';
     constructor(from: any, to: any, stepSize: any, reason: any) {
         super(`slice arguments slice(${from}, ${to}, ${stepSize}) invalid: ${reason}`);
         Object.setPrototypeOf(this, InvalidSliceError.prototype);
     }
 }
 
-export class NegativeStepError extends Error {
+export class NegativeStepError extends Error implements ZarrError {
+    __zarr__ = 'NegativeStepError';
     constructor() {
         super(`Negative step size is not supported when indexing.`);
         Object.setPrototypeOf(this, NegativeStepError.prototype);
     }
 }
 
-export class ValueError extends Error {
+export class ValueError extends Error implements ZarrError {
+    __zarr__ = 'ValueError';
     constructor(message: string) {
         super(message);
         Object.setPrototypeOf(this, ValueError.prototype);
     }
 }
 
-export class HTTPError extends Error {
+export class HTTPError extends Error implements ZarrError {
+    __zarr__ = 'HTTPError';
     constructor(code: string) {
-      super(code);
-      Object.setPrototypeOf(this, HTTPError.prototype);
+        super(code);
+        Object.setPrototypeOf(this, HTTPError.prototype);
     }
-  }
+}