diff --git a/packages/shell-api/src/shell-bson.spec.ts b/packages/shell-api/src/shell-bson.spec.ts
index 3d112da28..de656c6a7 100644
--- a/packages/shell-api/src/shell-bson.spec.ts
+++ b/packages/shell-api/src/shell-bson.spec.ts
@@ -381,6 +381,15 @@ describe('Shell BSON', function () {
       }
       expect.fail('expected error');
     });
+    it('passes through non-string args to `new Date()`', function () {
+      expect(shellBson.ISODate()).to.be.an.instanceOf(Date);
+      expect(shellBson.ISODate(0).getTime()).to.equal(0);
+      expect(shellBson.ISODate(null).getTime()).to.equal(0);
+      expect(shellBson.ISODate(1234).getTime()).to.equal(1234);
+      expect(shellBson.ISODate(shellBson.ISODate(1234)).getTime()).to.equal(
+        1234
+      );
+    });
   });
   describe('BinData', function () {
     it('expects strings as base 64', function () {
diff --git a/packages/shell-api/src/shell-bson.ts b/packages/shell-api/src/shell-bson.ts
index bdfd7b6cc..8ae1b375d 100644
--- a/packages/shell-api/src/shell-bson.ts
+++ b/packages/shell-api/src/shell-bson.ts
@@ -261,8 +261,11 @@ export default function constructShellBson(
       },
       { prototype: bson.Long.prototype }
     ),
-    ISODate: function ISODate(input?: string): Date {
-      if (!input) input = new Date().toISOString();
+    ISODate: function ISODate(
+      input?: string | number | Date | undefined
+    ): Date {
+      if (input === undefined) return new Date();
+      if (typeof input !== 'string') return new Date(input);
       const isoDateRegex =
         /^(?<Y>\d{4})-?(?<M>\d{2})-?(?<D>\d{2})([T ](?<h>\d{2})(:?(?<m>\d{2})(:?((?<s>\d{2})(\.(?<ms>\d+))?))?)?(?<tz>Z|([+-])(\d{2}):?(\d{2})?)?)?$/;
       const match = isoDateRegex.exec(input);