diff --git a/src/bson.ts b/src/bson.ts
index 8ec644bf..962e69e0 100644
--- a/src/bson.ts
+++ b/src/bson.ts
@@ -50,7 +50,7 @@ export {
   Decimal128
 };
 export { BSONValue } from './bson_value';
-export { BSONError, BSONVersionError } from './error';
+export { BSONError, BSONVersionError, BSONRuntimeError } from './error';
 export { BSONType } from './constants';
 export { EJSON } from './extended_json';
 
diff --git a/src/error.ts b/src/error.ts
index b01cde53..f98f0fb7 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -2,7 +2,11 @@ import { BSON_MAJOR_VERSION } from './constants';
 
 /**
  * @public
- * `BSONError` objects are thrown when runtime errors occur.
+ * @category Error
+ *
+ * `BSONError` objects are thrown when BSON ecounters an error.
+ *
+ * This is the parent class for all the other errors thrown by this library.
  */
 export class BSONError extends Error {
   /**
@@ -46,7 +50,10 @@ export class BSONError extends Error {
   }
 }
 
-/** @public */
+/**
+ * @public
+ * @category Error
+ */
 export class BSONVersionError extends BSONError {
   get name(): 'BSONVersionError' {
     return 'BSONVersionError';
@@ -58,3 +65,21 @@ export class BSONVersionError extends BSONError {
     );
   }
 }
+
+/**
+ * @public
+ * @category Error
+ *
+ * An error generated when BSON functions encounter an unexpected input
+ * or reaches an unexpected/invalid internal state
+ *
+ */
+export class BSONRuntimeError extends BSONError {
+  get name(): 'BSONRuntimeError' {
+    return 'BSONRuntimeError';
+  }
+
+  constructor(message: string) {
+    super(message);
+  }
+}
diff --git a/src/extended_json.ts b/src/extended_json.ts
index d0b60131..fd1f0a30 100644
--- a/src/extended_json.ts
+++ b/src/extended_json.ts
@@ -11,7 +11,7 @@ import {
 import { DBRef, isDBRefLike } from './db_ref';
 import { Decimal128 } from './decimal128';
 import { Double } from './double';
-import { BSONError, BSONVersionError } from './error';
+import { BSONError, BSONRuntimeError, BSONVersionError } from './error';
 import { Int32 } from './int_32';
 import { Long } from './long';
 import { MaxKey } from './max_key';
@@ -125,10 +125,14 @@ function deserializeValue(value: any, options: EJSONOptions = {}) {
     if (options.legacy) {
       if (typeof d === 'number') date.setTime(d);
       else if (typeof d === 'string') date.setTime(Date.parse(d));
+      else if (typeof d === 'bigint') date.setTime(Number(d));
+      else throw new BSONRuntimeError(`Unrecognized type for EJSON date: ${typeof d}`);
     } else {
       if (typeof d === 'string') date.setTime(Date.parse(d));
       else if (Long.isLong(d)) date.setTime(d.toNumber());
       else if (typeof d === 'number' && options.relaxed) date.setTime(d);
+      else if (typeof d === 'bigint') date.setTime(Number(d));
+      else throw new BSONRuntimeError(`Unrecognized type for EJSON date: ${typeof d}`);
     }
     return date;
   }
diff --git a/test/node/error.test.ts b/test/node/error.test.ts
index 8e1e7289..ee854368 100644
--- a/test/node/error.test.ts
+++ b/test/node/error.test.ts
@@ -1,7 +1,7 @@
 import { expect } from 'chai';
 import { loadESModuleBSON } from '../load_bson';
 
-import { __isWeb__, BSONError, BSONVersionError } from '../register-bson';
+import { __isWeb__, BSONError, BSONVersionError, BSONRuntimeError } from '../register-bson';
 
 const instanceOfChecksWork = !__isWeb__;
 
@@ -92,4 +92,14 @@ describe('BSONError', function () {
       expect(new BSONVersionError()).to.have.property('name', 'BSONVersionError');
     });
   });
+
+  describe('class BSONRuntimeError', function () {
+    it('is a BSONError instance', function () {
+      expect(BSONError.isBSONError(new BSONRuntimeError('Oopsie'))).to.be.true;
+    });
+
+    it('has a name property equal to "BSONRuntimeError"', function () {
+      expect(new BSONRuntimeError('Woops!')).to.have.property('name', 'BSONRuntimeError');
+    });
+  });
 });
diff --git a/test/node/exports.test.ts b/test/node/exports.test.ts
index ac258c20..2f800729 100644
--- a/test/node/exports.test.ts
+++ b/test/node/exports.test.ts
@@ -26,6 +26,7 @@ const EXPECTED_EXPORTS = [
   'BSONRegExp',
   'Decimal128',
   'BSONError',
+  'BSONRuntimeError',
   'setInternalBufferSize',
   'serialize',
   'serializeWithBufferAndIndex',
diff --git a/test/node/extended_json.test.ts b/test/node/extended_json.test.ts
index 51e19fd7..c1f14f2d 100644
--- a/test/node/extended_json.test.ts
+++ b/test/node/extended_json.test.ts
@@ -2,7 +2,7 @@ import * as BSON from '../register-bson';
 const EJSON = BSON.EJSON;
 import * as vm from 'node:vm';
 import { expect } from 'chai';
-import { BSONVersionError } from '../../src';
+import { BSONVersionError, BSONRuntimeError } from '../../src';
 
 // BSON types
 const Binary = BSON.Binary;
@@ -440,6 +440,29 @@ describe('Extended JSON', function () {
             expect(bson).to.deep.equal(doc);
           });
         });
+
+        context('when using useBigInt64=true', function () {
+          it('parses $date.$numberLong with millis since epoch', function () {
+            if (BSON.__noBigInt__) {
+              this.skip();
+            }
+            const date = new Date(1676315495987);
+            const doc = { field: date };
+            const stringified = EJSON.stringify(doc, { relaxed: false });
+            const parsedDoc = EJSON.parse(stringified, { useBigInt64: true, relaxed: false });
+            expect(parsedDoc).to.deep.equal(doc);
+          });
+        });
+
+        context('when deserializing object with invalid $date key', function () {
+          it('throws a BSONRuntimeError', function () {
+            const doc = { field: { $date: new ArrayBuffer(10) } };
+            const s = EJSON.stringify(doc, { relaxed: false });
+            expect(() => {
+              EJSON.parse(s, { relaxed: false });
+            }).to.throw(BSONRuntimeError, /Unrecognized type/i);
+          });
+        });
       });
 
       context('when deserializing regex', function () {