diff --git a/lib/dash/dash_parser.js b/lib/dash/dash_parser.js
index 767ae8668c..89da858931 100644
--- a/lib/dash/dash_parser.js
+++ b/lib/dash/dash_parser.js
@@ -99,13 +99,13 @@ shaka.dash.DashParser = class {
      * Largest period start time seen.
      * @private {?number}
      */
-    this.largestPeriodId_ = null;
+    this.largestPeriodStartTime_ = null;
 
     /**
-     * Period start times seen in previous manifest.
+     * Period IDs seen in previous manifest.
      * @private {!Array.<number>}
      */
-    this.seenPeriodIds = [];
+    this.seenPeriodIds_ = [];
 
     /**
      * The minimum of the availabilityTimeOffset values among the adaptation
@@ -542,7 +542,6 @@ shaka.dash.DashParser = class {
         mpd, 'mediaPresentationDuration', XmlUtils.parseDuration);
 
     const periods = [];
-    const periodIds = [];
     let prevEnd = 0;
     const periodNodes = XmlUtils.findChildren(mpd, 'Period');
     // This uses a for-loop rather than a for-of loop because this needs to look
@@ -551,7 +550,7 @@ shaka.dash.DashParser = class {
     for (const {i, item: elem, next} of enumerate(periodNodes)) {
       const start = /** @type {number} */ (
         XmlUtils.parseAttr(elem, 'start', XmlUtils.parseDuration, prevEnd));
-      const periodId = Number(elem.id);
+      const periodId = elem.id;
       const givenDuration =
           XmlUtils.parseAttr(elem, 'duration', XmlUtils.parseDuration);
 
@@ -594,32 +593,31 @@ shaka.dash.DashParser = class {
        *
        * Skip periods that match all of the following criteria:
        * - Start time is earlier than latest period start time ever seen
-       * - Start time is never seen in the previous manifest
+       * - Period ID is never seen in the previous manifest
        * - Not the last period in the manifest
        *
        * Periods that meet the aforementioned criteria are considered invalid
        * and should be safe to discard.
        */
-      if (this.largestPeriodId_ !== null && periodId !== null) {
-        if (periodId < this.largestPeriodId_ &&
-          !this.seenPeriodIds.includes(periodId) &&
-          i + 1 != periodNodes.length) {
-          shaka.log.debug(
-              `Skipping Period ${i+1} as its period ID is smaller than ` +
-              'the largest period ID that has been seen, and ID ' +
-              'is unseen before');
-          continue;
-        } else {
-          periodIds.push(periodId);
-        }
+
+      if (this.largestPeriodStartTime_ !== null &&
+        periodId !== null && start !== null &&
+        start < this.largestPeriodStartTime_ &&
+        !this.seenPeriodIds_.includes(periodId) &&
+        i + 1 != periodNodes.length) {
+        shaka.log.debug(
+            `Skipping Period with ID ${periodId} as its start time is smaller` +
+            ' than the largest period start time that has been seen, and ID ' +
+            'is unseen before');
+        continue;
       }
 
 
       // Save maximum period start time if it is the last period
-      if (periodId !== null &&
-          (this.largestPeriodId_ === null ||
-            periodId > this.largestPeriodId_)) {
-        this.largestPeriodId_ = periodId;
+      if (start !== null &&
+        (this.largestPeriodStartTime_ === null ||
+          start > this.largestPeriodStartTime_)) {
+        this.largestPeriodStartTime_ = start;
       }
 
       // Parse child nodes.
@@ -653,8 +651,8 @@ shaka.dash.DashParser = class {
       prevEnd = start + periodDuration;
     } // end of period parsing loop
 
-    // Replace previous seen start time with the current one.
-    this.seenPeriodIds = periodIds;
+    // Replace previous seen periods with the current one.
+    this.seenPeriodIds_ = periods.map((el) => el.id);
 
     if (presentationDuration != null) {
       if (prevEnd != presentationDuration) {
diff --git a/test/dash/dash_parser_manifest_unit.js b/test/dash/dash_parser_manifest_unit.js
index 10e6758b5c..6b5784e8d3 100644
--- a/test/dash/dash_parser_manifest_unit.js
+++ b/test/dash/dash_parser_manifest_unit.js
@@ -2155,7 +2155,7 @@ describe('DashParser Manifest', () => {
      * @param {!Array.<number>} periods Start time of multiple periods
      * @return {string}
      */
-  function buildManifestWithPeriodId(periods) {
+  function buildManifestWithPeriodStartTime(periods) {
     const mpdTemplate = [
       `<MPD type="dynamic"`,
       'availabilityStartTime="1970-01-01T00:00:00Z"',
@@ -2179,6 +2179,8 @@ describe('DashParser Manifest', () => {
     };
     const periodXmls = periods.map((period, i) => {
       const duration = i+1 === periods.length ? 10 : periods[i+1] - period;
+      // Period start time as ID here. If we use index then there will be
+      // periods with same period ID and different start time which are invalid.
       return periodTemplate(period, period, duration);
     });
     return sprintf(mpdTemplate, {
@@ -2195,9 +2197,9 @@ describe('DashParser Manifest', () => {
 
   it('skip periods that are earlier than max period start time', async () => {
     const sources = [
-      buildManifestWithPeriodId([5, 15]),
-      buildManifestWithPeriodId([6, 15]), // simulate out-of-sync of -1s
-      buildManifestWithPeriodId([4, 15]), // simulate out-of-sync of +1s
+      buildManifestWithPeriodStartTime([5, 15]),
+      buildManifestWithPeriodStartTime([6, 15]), // simulate out-of-sync of +1s
+      buildManifestWithPeriodStartTime([4, 15]), // simulate out-of-sync of -1s
     ];
     const segments = [];