diff --git a/lib/error.js b/lib/error.js
index cd5f8e4..1a6d054 100644
--- a/lib/error.js
+++ b/lib/error.js
@@ -8,16 +8,30 @@ const createError = (name, message, status = null, cause = null, request = null)
   return error;
 };
 
-// Create specific error types using the factory function
-const ValidationError = (message) => createError('ValidationError', message);
+// Create specific error types using the factory function.
+// These must be `function` declarations, not arrow functions: they are
+// invoked with `new` (see Methods.js and onfleet.js), and arrow functions
+// have no [[Construct]] behavior, so `new` on one throws
+// "X is not a constructor".
+function ValidationError(message) {
+  return createError('ValidationError', message);
+}
 
-const PermissionError = (message, status, cause, request) => createError('PermissionError', message, status, cause, request);
+function PermissionError(message, status, cause, request) {
+  return createError('PermissionError', message, status, cause, request);
+}
 
-const HttpError = (message, status, cause, request) => createError('HttpError', message, status, cause, request);
+function HttpError(message, status, cause, request) {
+  return createError('HttpError', message, status, cause, request);
+}
 
-const RateLimitError = (message, status, cause, request) => createError('RateLimitError', message, status, cause, request);
+function RateLimitError(message, status, cause, request) {
+  return createError('RateLimitError', message, status, cause, request);
+}
 
-const ServiceError = (message, status, cause, request) => createError('ServiceError', message, status, cause, request);
+function ServiceError(message, status, cause, request) {
+  return createError('ServiceError', message, status, cause, request);
+}
 
 // Export the custom error creators
 export {
diff --git a/test/test.js b/test/test.js
index 7331596..1c9fc11 100644
--- a/test/test.js
+++ b/test/test.js
@@ -471,3 +471,94 @@ describe('Additional resource coverage', () => {
       assert.equal(res, 200);
     }));
 });
+
+describe('Error handling testing', () => {
+  const onfleet = new Onfleet(apiKey);
+
+  afterEach(() => {
+    nock.cleanAll();
+  });
+
+  const errorBody = (error, message = 'Something went wrong') => ({
+    message: {
+      message,
+      error,
+      cause: null,
+      request: null,
+    },
+  });
+
+  it('ValidationError - constructing without an API key', () => {
+    expect(() => new Onfleet()).to.throw(Error).with.property('name', 'ValidationError');
+  });
+
+  it('RateLimitError - error code 2300 raises a RateLimitError, not a TypeError', () => {
+    nock(baseUrl)
+      .post((uri) => uri.includes('tasks'))
+      .reply(429, errorBody(2300, 'Rate limit exceeded'));
+
+    return expect(onfleet.tasks.create({}))
+      .to.be.rejected
+      .then((error) => {
+        expect(error).to.not.be.instanceOf(TypeError);
+        assert.equal(error.name, 'RateLimitError');
+        assert.equal(error.message, 'Rate limit exceeded');
+      });
+  });
+
+  it('PermissionError - error code in the 1100-1108 range raises a PermissionError', () => {
+    nock(baseUrl)
+      .post((uri) => uri.includes('tasks'))
+      .reply(403, errorBody(1104, 'Insufficient permissions'));
+
+    return expect(onfleet.tasks.create({}))
+      .to.be.rejected
+      .then((error) => {
+        expect(error).to.not.be.instanceOf(TypeError);
+        assert.equal(error.name, 'PermissionError');
+        assert.equal(error.message, 'Insufficient permissions');
+      });
+  });
+
+  it('ServiceError - error code >= 2500 raises a ServiceError', () => {
+    nock(baseUrl)
+      .post((uri) => uri.includes('tasks'))
+      .reply(500, errorBody(2500, 'Internal service error'));
+
+    return expect(onfleet.tasks.create({}))
+      .to.be.rejected
+      .then((error) => {
+        expect(error).to.not.be.instanceOf(TypeError);
+        assert.equal(error.name, 'ServiceError');
+        assert.equal(error.message, 'Internal service error');
+      });
+  });
+
+  it('ServiceError - error code 2218 (Auto-Dispatch precondition) raises a ServiceError', () => {
+    nock(baseUrl)
+      .post((uri) => uri.includes('tasks'))
+      .reply(412, errorBody(2218, 'Auto-Dispatch precondition failed'));
+
+    return expect(onfleet.tasks.create({}))
+      .to.be.rejected
+      .then((error) => {
+        expect(error).to.not.be.instanceOf(TypeError);
+        assert.equal(error.name, 'ServiceError');
+        assert.equal(error.message, 'Auto-Dispatch precondition failed');
+      });
+  });
+
+  it('HttpError - any other error code raises a generic HttpError', () => {
+    nock(baseUrl)
+      .post((uri) => uri.includes('tasks'))
+      .reply(400, errorBody(1000, 'Bad request'));
+
+    return expect(onfleet.tasks.create({}))
+      .to.be.rejected
+      .then((error) => {
+        expect(error).to.not.be.instanceOf(TypeError);
+        assert.equal(error.name, 'HttpError');
+        assert.equal(error.message, 'Bad request');
+      });
+  });
+});