diff --git a/lib/dash/dash_parser.js b/lib/dash/dash_parser.js
index cfa269e302..3b92d89d13 100644
--- a/lib/dash/dash_parser.js
+++ b/lib/dash/dash_parser.js
@@ -1278,55 +1278,56 @@ shaka.dash.DashParser = class {
         context.period.id + ',' + context.representation.id : '';
 
     /** @type {shaka.extern.Stream} */
-    const stream = {
-      id: this.globalId_++,
-      originalId: context.representation.id,
-      createSegmentIndex: async () => {
-        // If we have a stream with the same context id stored in the map
-        // that has no segmentIndex, we should set the segmentIndex for it.
-        const storedInMap = contextId && context.dynamic &&
-              this.streamMap_[contextId];
-
-        const currentStream = storedInMap ? this.streamMap_[contextId] : stream;
-        if (!currentStream.segmentIndex) {
-          currentStream.segmentIndex = await streamInfo.generateSegmentIndex();
-        }
-      },
+    let stream;
 
-      closeSegmentIndex: () => {
-        if (stream.segmentIndex) {
-          stream.segmentIndex.release();
-          stream.segmentIndex = null;
-        }
-      },
-      segmentIndex: null,
-      mimeType: context.representation.mimeType,
-      codecs: context.representation.codecs,
-      frameRate: context.representation.frameRate,
-      pixelAspectRatio: context.representation.pixelAspectRatio,
-      bandwidth: context.bandwidth,
-      width: context.representation.width,
-      height: context.representation.height,
-      kind,
-      encrypted: contentProtection.drmInfos.length > 0,
-      drmInfos: contentProtection.drmInfos,
-      keyIds,
-      language,
-      label,
-      type: context.adaptationSet.contentType,
-      primary: isPrimary,
-      trickModeVideo: null,
-      emsgSchemeIdUris:
-          context.representation.emsgSchemeIdUris,
-      roles,
-      forced: forced,
-      channelsCount: context.representation.numChannels,
-      audioSamplingRate: context.representation.audioSamplingRate,
-      spatialAudio: spatialAudio,
-      closedCaptions,
-      hdr,
-      tilesLayout,
-      matchedStreams: [],
+    if (contextId && this.streamMap_[contextId]) {
+      stream = this.streamMap_[contextId];
+    } else {
+      stream = {
+        id: this.globalId_++,
+        originalId: context.representation.id,
+        createSegmentIndex: () => Promise.resolve(),
+        closeSegmentIndex: () => {
+          if (stream.segmentIndex) {
+            stream.segmentIndex.release();
+            stream.segmentIndex = null;
+          }
+        },
+        segmentIndex: null,
+        mimeType: context.representation.mimeType,
+        codecs: context.representation.codecs,
+        frameRate: context.representation.frameRate,
+        pixelAspectRatio: context.representation.pixelAspectRatio,
+        bandwidth: context.bandwidth,
+        width: context.representation.width,
+        height: context.representation.height,
+        kind,
+        encrypted: contentProtection.drmInfos.length > 0,
+        drmInfos: contentProtection.drmInfos,
+        keyIds,
+        language,
+        label,
+        type: context.adaptationSet.contentType,
+        primary: isPrimary,
+        trickModeVideo: null,
+        emsgSchemeIdUris:
+            context.representation.emsgSchemeIdUris,
+        roles,
+        forced,
+        channelsCount: context.representation.numChannels,
+        audioSamplingRate: context.representation.audioSamplingRate,
+        spatialAudio,
+        closedCaptions,
+        hdr,
+        tilesLayout,
+        matchedStreams: [],
+      };
+    }
+
+    stream.createSegmentIndex = async () => {
+      if (!stream.segmentIndex) {
+        stream.segmentIndex = await streamInfo.generateSegmentIndex();
+      }
     };
 
     if (contextId && context.dynamic && !this.streamMap_[contextId]) {
diff --git a/lib/util/periods.js b/lib/util/periods.js
index bb1b027d0e..40559a2336 100644
--- a/lib/util/periods.js
+++ b/lib/util/periods.js
@@ -671,11 +671,11 @@ shaka.util.PeriodCombiner = class {
     // Also checks if the segmentIndex is still valid after the async
     // operations, to make sure we stop if the active stream has changed.
     if (outputStream.segmentIndex instanceof shaka.media.MetaSegmentIndex) {
-      for (let i = 0; i < streams.length; i++) {
+      for (let i = firstNewPeriodIndex; i < streams.length; i++) {
         const match = streams[i];
-        if (match.segmentIndex && i >= firstNewPeriodIndex) {
-          goog.asserts.assert(match.segmentIndex,
-              'stream should have a segmentIndex.');
+        goog.asserts.assert(match.segmentIndex,
+            'stream should have a segmentIndex.');
+        if (match.segmentIndex) {
           outputStream.segmentIndex.appendSegmentIndex(match.segmentIndex);
         }
       }