diff --git a/src/error.ts b/src/error.ts
index cfd70f32aa..02170dcd87 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -625,6 +625,8 @@ export class MongoSystemError extends MongoError {
     if (reason) {
       this.reason = reason;
     }
+
+    this.code = reason.error?.code;
   }
 
   get name(): string {
diff --git a/src/index.ts b/src/index.ts
index 27c8ac944c..0502109519 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -62,6 +62,7 @@ export {
   MongoServerError,
   MongoServerSelectionError,
   MongoSystemError,
+  MongoTailableCursorError,
   MongoTopologyClosedError,
   MongoTransactionError,
   MongoWriteConcernError
diff --git a/test/unit/error.test.js b/test/unit/error.test.ts
similarity index 75%
rename from test/unit/error.test.js
rename to test/unit/error.test.ts
index 134d309aa8..2bdb5f8479 100644
--- a/test/unit/error.test.js
+++ b/test/unit/error.test.ts
@@ -1,53 +1,77 @@
-/* eslint no-empty: ["error", { "allowEmptyCatch": true }] */
-'use strict';
-
-const expect = require('chai').expect;
-const mock = require('../tools/mongodb-mock/index');
-const { getSymbolFrom } = require('../tools/utils');
-const { ReplSetFixture } = require('../tools/common');
-const { ns, isHello } = require('../../src/utils');
-const { Topology } = require('../../src/sdam/topology');
-const {
-  MongoNetworkError,
-  MongoWriteConcernError,
+import { expect } from 'chai';
+
+import {
+  PoolClosedError as MongoPoolClosedError,
+  WaitQueueTimeoutError as MongoWaitQueueTimeoutError
+} from '../../src/cmap/errors';
+import {
+  isRetryableEndTransactionError,
+  isSDAMUnrecoverableError,
+  LEGACY_NOT_PRIMARY_OR_SECONDARY_ERROR_MESSAGE,
+  LEGACY_NOT_WRITABLE_PRIMARY_ERROR_MESSAGE,
+  MongoSystemError,
+  NODE_IS_RECOVERING_ERROR_MESSAGE
+} from '../../src/error';
+import * as importsFromErrorSrc from '../../src/error';
+import {
   MongoError,
+  MongoNetworkError,
+  MongoParseError,
   MongoServerError,
-  MongoParseError
-} = require('../../src/index');
-const {
-  LEGACY_NOT_WRITABLE_PRIMARY_ERROR_MESSAGE,
-  LEGACY_NOT_PRIMARY_OR_SECONDARY_ERROR_MESSAGE,
-  NODE_IS_RECOVERING_ERROR_MESSAGE,
-  isRetryableEndTransactionError,
-  isSDAMUnrecoverableError
-} = require('../../src/error');
-const {
-  PoolClosedError: MongoPoolClosedError,
-  WaitQueueTimeoutError: MongoWaitQueueTimeoutError
-} = require('../../src/cmap/errors');
+  MongoWriteConcernError,
+  TopologyDescription
+} from '../../src/index';
+import * as importsFromEntryPoint from '../../src/index';
+import { Topology, TopologyOptions } from '../../src/sdam/topology';
+import { isHello, ns, setDifference } from '../../src/utils';
+import { ReplSetFixture } from '../tools/common';
+import { cleanup } from '../tools/mongodb-mock/index';
+import { getSymbolFrom } from '../tools/utils';
 
 describe('MongoErrors', () => {
-  // import errors as object
-  let errorClasses = Object.fromEntries(
-    Object.entries(require('../../src/index')).filter(([key]) => key.endsWith('Error'))
+  let errorClassesFromEntryPoint = Object.fromEntries(
+    Object.entries(importsFromEntryPoint).filter(
+      ([key, value]) => key.endsWith('Error') && value.toString().startsWith('class')
+    )
+  ) as any;
+  errorClassesFromEntryPoint = {
+    ...errorClassesFromEntryPoint,
+    MongoPoolClosedError,
+    MongoWaitQueueTimeoutError
+  };
+
+  const errorClassesFromErrorSrc = Object.fromEntries(
+    Object.entries(importsFromErrorSrc).filter(
+      ([key, value]) => key.endsWith('Error') && value.toString().startsWith('class')
+    )
   );
-  errorClasses = { ...errorClasses, MongoPoolClosedError, MongoWaitQueueTimeoutError };
 
-  for (const errorName in errorClasses) {
-    describe(errorName, () => {
-      it(`name should be read-only`, () => {
+  it('all defined errors should be public', () => {
+    expect(
+      setDifference(Object.keys(errorClassesFromEntryPoint), Object.keys(errorClassesFromErrorSrc))
+    ).to.have.property('size', 3);
+
+    expect(
+      setDifference(Object.keys(errorClassesFromErrorSrc), Object.keys(errorClassesFromEntryPoint))
+    ).to.have.property('size', 0);
+  });
+
+  describe('error names should be read-only', () => {
+    for (const [errorName, errorClass] of Object.entries(errorClassesFromEntryPoint)) {
+      it(`${errorName} should be read-only`, () => {
         // Dynamically create error class with message
-        let error = new errorClasses[errorName]('generated by test');
+        const error = new (errorClass as any)('generated by test', {});
         // expect name property to be class name
         expect(error).to.have.property('name', errorName);
 
         try {
           error.name = 'renamed by test';
+          // eslint-disable-next-line no-empty
         } catch (err) {}
         expect(error).to.have.property('name', errorName);
       });
-    });
-  }
+    }
+  });
 
   describe('MongoError#constructor', () => {
     it('should accept a string', function () {
@@ -89,6 +113,39 @@ describe('MongoErrors', () => {
     });
   });
 
+  describe('MongoSystemError#constructor', () => {
+    context('when the topology description contains an error code', () => {
+      it('contains the specified code as a top level property', () => {
+        const topologyDescription = {
+          error: {
+            code: 123
+          }
+        } as TopologyDescription;
+
+        const error = new MongoSystemError('something went wrong', topologyDescription);
+        expect(error).to.haveOwnProperty('code', 123);
+      });
+    });
+
+    context('when the topology description does not contain an error code', () => {
+      it('contains the code as a top level property that is undefined', () => {
+        const topologyDescription = { error: {} } as TopologyDescription;
+
+        const error = new MongoSystemError('something went wrong', topologyDescription);
+        expect(error).to.haveOwnProperty('code', undefined);
+      });
+    });
+
+    context('when the topology description does not contain an error property', () => {
+      it('contains the code as a top level property that is undefined', () => {
+        const topologyDescription = {} as TopologyDescription;
+
+        const error = new MongoSystemError('something went wrong', topologyDescription);
+        expect(error).to.haveOwnProperty('code', undefined);
+      });
+    });
+  });
+
   describe('#isRetryableEndTransactionError', function () {
     context('when the error has a RetryableWriteError label', function () {
       const error = new MongoNetworkError('');
@@ -202,7 +259,10 @@ describe('MongoErrors', () => {
       const errorWithOptionFalse = new MongoNetworkError('', { beforeHandshake: false });
       expect(getSymbolFrom(errorWithOptionFalse, 'beforeHandshake', false)).to.be.a('symbol');
 
-      const errorWithBadOption = new MongoNetworkError('', { beforeHandshake: 'not boolean' });
+      const errorWithBadOption = new MongoNetworkError('', {
+        // @ts-expect-error: beforeHandshake must be a boolean value
+        beforeHandshake: 'not boolean'
+      });
       expect(getSymbolFrom(errorWithBadOption, 'beforeHandshake', false)).to.be.an('undefined');
 
       const errorWithoutOption = new MongoNetworkError('');
@@ -254,14 +314,14 @@ describe('MongoErrors', () => {
     };
 
     before(() => (test = new ReplSetFixture()));
-    afterEach(() => mock.cleanup());
+    afterEach(() => cleanup());
     beforeEach(() => test.setup());
 
     function makeAndConnectReplSet(cb) {
       let invoked = false;
       const replSet = new Topology(
         [test.primaryServer.hostAddress(), test.firstSecondaryServer.hostAddress()],
-        { replicaSet: 'rs' }
+        { replicaSet: 'rs' } as TopologyOptions
       );
 
       replSet.once('error', err => {