diff --git a/polyfill/test/plaindatetime.mjs b/polyfill/test/plaindatetime.mjs
index b3a83589f0..fddf00d284 100644
--- a/polyfill/test/plaindatetime.mjs
+++ b/polyfill/test/plaindatetime.mjs
@@ -546,154 +546,6 @@ describe('DateTime', () => {
       equal(`${dt1.since(dt2, { smallestUnit: 'years', roundingMode: 'halfExpand' })}`, '-P2Y');
     });
   });
-  describe('DateTime.round works', () => {
-    const dt = PlainDateTime.from('1976-11-18T14:23:30.123456789');
-    it('throws without parameter', () => {
-      throws(() => dt.round(), TypeError);
-    });
-    it('throws without required smallestUnit parameter', () => {
-      throws(() => dt.round({}), RangeError);
-      throws(() => dt.round({ roundingIncrement: 1, roundingMode: 'ceil' }), RangeError);
-    });
-    it('throws on disallowed or invalid smallestUnit (object param)', () => {
-      ['era', 'year', 'month', 'week', 'years', 'months', 'weeks', 'nonsense'].forEach((smallestUnit) => {
-        throws(() => dt.round({ smallestUnit }), RangeError);
-      });
-    });
-    it('throws on disallowed or invalid smallestUnit (string param)', () => {
-      ['era', 'year', 'month', 'week', 'years', 'months', 'weeks', 'nonsense'].forEach((smallestUnit) => {
-        throws(() => dt.round(smallestUnit), RangeError);
-      });
-    });
-    it('throws on invalid roundingMode', () => {
-      throws(() => dt.round({ smallestUnit: 'second', roundingMode: 'cile' }), RangeError);
-    });
-    const incrementOneNearest = [
-      ['day', '1976-11-19T00:00:00'],
-      ['hour', '1976-11-18T14:00:00'],
-      ['minute', '1976-11-18T14:24:00'],
-      ['second', '1976-11-18T14:23:30'],
-      ['millisecond', '1976-11-18T14:23:30.123'],
-      ['microsecond', '1976-11-18T14:23:30.123457'],
-      ['nanosecond', '1976-11-18T14:23:30.123456789']
-    ];
-    incrementOneNearest.forEach(([smallestUnit, expected]) => {
-      it(`rounds to nearest ${smallestUnit}`, () =>
-        equal(`${dt.round({ smallestUnit, roundingMode: 'halfExpand' })}`, expected));
-    });
-    const incrementOneCeil = [
-      ['day', '1976-11-19T00:00:00'],
-      ['hour', '1976-11-18T15:00:00'],
-      ['minute', '1976-11-18T14:24:00'],
-      ['second', '1976-11-18T14:23:31'],
-      ['millisecond', '1976-11-18T14:23:30.124'],
-      ['microsecond', '1976-11-18T14:23:30.123457'],
-      ['nanosecond', '1976-11-18T14:23:30.123456789']
-    ];
-    incrementOneCeil.forEach(([smallestUnit, expected]) => {
-      it(`rounds up to ${smallestUnit}`, () => equal(`${dt.round({ smallestUnit, roundingMode: 'ceil' })}`, expected));
-    });
-    const incrementOneFloor = [
-      ['day', '1976-11-18T00:00:00'],
-      ['hour', '1976-11-18T14:00:00'],
-      ['minute', '1976-11-18T14:23:00'],
-      ['second', '1976-11-18T14:23:30'],
-      ['millisecond', '1976-11-18T14:23:30.123'],
-      ['microsecond', '1976-11-18T14:23:30.123456'],
-      ['nanosecond', '1976-11-18T14:23:30.123456789']
-    ];
-    incrementOneFloor.forEach(([smallestUnit, expected]) => {
-      it(`rounds down to ${smallestUnit}`, () =>
-        equal(`${dt.round({ smallestUnit, roundingMode: 'floor' })}`, expected));
-      it(`truncates to ${smallestUnit}`, () => equal(`${dt.round({ smallestUnit, roundingMode: 'trunc' })}`, expected));
-    });
-    it('halfExpand is the default', () => {
-      equal(`${dt.round({ smallestUnit: 'minute' })}`, '1976-11-18T14:24:00');
-      equal(`${dt.round({ smallestUnit: 'second' })}`, '1976-11-18T14:23:30');
-    });
-    it('rounding down is towards the Big Bang, not towards 1 BCE', () => {
-      const dt2 = PlainDateTime.from('-000099-12-15T12:00:00.5');
-      const smallestUnit = 'second';
-      equal(`${dt2.round({ smallestUnit, roundingMode: 'ceil' })}`, '-000099-12-15T12:00:01');
-      equal(`${dt2.round({ smallestUnit, roundingMode: 'floor' })}`, '-000099-12-15T12:00:00');
-      equal(`${dt2.round({ smallestUnit, roundingMode: 'trunc' })}`, '-000099-12-15T12:00:00');
-      equal(`${dt2.round({ smallestUnit, roundingMode: 'halfExpand' })}`, '-000099-12-15T12:00:01');
-    });
-    it('rounds to an increment of hours', () => {
-      equal(`${dt.round({ smallestUnit: 'hour', roundingIncrement: 4 })}`, '1976-11-18T16:00:00');
-    });
-    it('rounds to an increment of minutes', () => {
-      equal(`${dt.round({ smallestUnit: 'minute', roundingIncrement: 15 })}`, '1976-11-18T14:30:00');
-    });
-    it('rounds to an increment of seconds', () => {
-      equal(`${dt.round({ smallestUnit: 'second', roundingIncrement: 30 })}`, '1976-11-18T14:23:30');
-    });
-    it('rounds to an increment of milliseconds', () => {
-      equal(`${dt.round({ smallestUnit: 'millisecond', roundingIncrement: 10 })}`, '1976-11-18T14:23:30.12');
-    });
-    it('rounds to an increment of microseconds', () => {
-      equal(`${dt.round({ smallestUnit: 'microsecond', roundingIncrement: 10 })}`, '1976-11-18T14:23:30.12346');
-    });
-    it('rounds to an increment of nanoseconds', () => {
-      equal(`${dt.round({ smallestUnit: 'nanosecond', roundingIncrement: 10 })}`, '1976-11-18T14:23:30.12345679');
-    });
-    it('1 day is a valid increment', () => {
-      equal(`${dt.round({ smallestUnit: 'day', roundingIncrement: 1 })}`, '1976-11-19T00:00:00');
-    });
-    it('valid hour increments divide into 24', () => {
-      const smallestUnit = 'hour';
-      [1, 2, 3, 4, 6, 8, 12].forEach((roundingIncrement) => {
-        assert(dt.round({ smallestUnit, roundingIncrement }) instanceof PlainDateTime);
-      });
-    });
-    ['minute', 'second'].forEach((smallestUnit) => {
-      it(`valid ${smallestUnit} increments divide into 60`, () => {
-        [1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30].forEach((roundingIncrement) => {
-          assert(dt.round({ smallestUnit, roundingIncrement }) instanceof PlainDateTime);
-        });
-      });
-    });
-    ['millisecond', 'microsecond', 'nanosecond'].forEach((smallestUnit) => {
-      it(`valid ${smallestUnit} increments divide into 1000`, () => {
-        [1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500].forEach((roundingIncrement) => {
-          assert(dt.round({ smallestUnit, roundingIncrement }) instanceof PlainDateTime);
-        });
-      });
-    });
-    it('throws on increments that do not divide evenly into the next highest', () => {
-      throws(() => dt.round({ smallestUnit: 'day', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'hour', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'minute', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'second', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'millisecond', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'microsecond', roundingIncrement: 29 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'nanosecond', roundingIncrement: 29 }), RangeError);
-    });
-    it('throws on increments that are equal to the next highest', () => {
-      throws(() => dt.round({ smallestUnit: 'hour', roundingIncrement: 24 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'minute', roundingIncrement: 60 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'second', roundingIncrement: 60 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'millisecond', roundingIncrement: 1000 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'microsecond', roundingIncrement: 1000 }), RangeError);
-      throws(() => dt.round({ smallestUnit: 'nanosecond', roundingIncrement: 1000 }), RangeError);
-    });
-    const bal = PlainDateTime.from('1976-11-18T23:59:59.999999999');
-    ['day', 'hour', 'minute', 'second', 'millisecond', 'microsecond'].forEach((smallestUnit) => {
-      it(`balances to next ${smallestUnit}`, () => {
-        equal(`${bal.round({ smallestUnit })}`, '1976-11-19T00:00:00');
-      });
-    });
-    it('accepts plural units', () => {
-      ['day', 'hour', 'minute', 'second', 'millisecond', 'microsecond', 'nanosecond'].forEach((smallestUnit) => {
-        assert(dt.round({ smallestUnit }).equals(dt.round({ smallestUnit: `${smallestUnit}s` })));
-      });
-    });
-    it('accepts string parameter as shortcut for {smallestUnit}', () => {
-      ['day', 'hour', 'minute', 'second', 'millisecond', 'microsecond', 'nanosecond'].forEach((smallestUnit) => {
-        assert(dt.round(smallestUnit).equals(dt.round({ smallestUnit })));
-      });
-    });
-  });
   describe('DateTime.from() works', () => {
     it('DateTime.from("1976-11-18 15:23:30")', () =>
       equal(`${PlainDateTime.from('1976-11-18 15:23:30')}`, '1976-11-18T15:23:30'));