diff --git a/packages/common/src/i18n/format_date.ts b/packages/common/src/i18n/format_date.ts
index 355298a60f..c9ecd65c20 100644
--- a/packages/common/src/i18n/format_date.ts
+++ b/packages/common/src/i18n/format_date.ts
@@ -734,7 +734,10 @@ export function isoStringToDate(match: RegExpMatchArray): Date {
   const h = Number(match[4] || 0) - tzHour;
   const m = Number(match[5] || 0) - tzMin;
   const s = Number(match[6] || 0);
-  const ms = Math.round(parseFloat('0.' + (match[7] || 0)) * 1000);
+  // The ECMAScript specification (https://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.11)
+  // defines that `DateTime` milliseconds should always be rounded down, so that `999.9ms`
+  // becomes `999ms`.
+  const ms = Math.floor(parseFloat('0.' + (match[7] || 0)) * 1000);
   timeSetter.call(date, h, m, s, ms);
   return date;
 }
diff --git a/packages/common/test/pipes/date_pipe_spec.ts b/packages/common/test/pipes/date_pipe_spec.ts
index ba532d5e25..21cf55ab7b 100644
--- a/packages/common/test/pipes/date_pipe_spec.ts
+++ b/packages/common/test/pipes/date_pipe_spec.ts
@@ -85,6 +85,13 @@ import {JitReflector} from '@angular/platform-browser-dynamic/src/compiler_refle
            expect(pipe.transform('2012-12-30T00:00:00', 'w')).toEqual('1');
            expect(pipe.transform('2012-12-31T00:00:00', 'w')).toEqual('1');
          });
+
+
+      it('should round milliseconds down to the nearest millisecond', () => {
+        expect(pipe.transform('2020-08-01T23:59:59.999', 'yyyy-MM-dd')).toEqual('2020-08-01');
+        expect(pipe.transform('2020-08-01T23:59:59.9999', 'yyyy-MM-dd, h:mm:ss SSS'))
+            .toEqual('2020-08-01, 11:59:59 999');
+      });
     });
   });
 }