diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/MaskingMediaSource.java b/library/core/src/main/java/com/google/android/exoplayer2/source/MaskingMediaSource.java
index 28d9369c83..35b3e1848e 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/MaskingMediaSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/source/MaskingMediaSource.java
@@ -234,7 +234,15 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
   @RequiresNonNull("unpreparedMaskingMediaPeriod")
   private void setPreparePositionOverrideToUnpreparedMaskingPeriod(long preparePositionOverrideUs) {
     MaskingMediaPeriod maskingPeriod = unpreparedMaskingMediaPeriod;
-    long periodDurationUs = timeline.getPeriodByUid(maskingPeriod.id.periodUid, period).durationUs;
+    int maskingPeriodIndex = timeline.getIndexOfPeriod(maskingPeriod.id.periodUid);
+    if (maskingPeriodIndex == C.INDEX_UNSET) {
+      // The new timeline doesn't contain this period anymore. This can happen if the media source
+      // has multiple periods and removed the first period with a timeline update. Ignore the
+      // update, as the non-existing period will be released anyway as soon as the player receives
+      // this new timeline.
+      return;
+    }
+    long periodDurationUs = timeline.getPeriod(maskingPeriodIndex, period).durationUs;
     if (periodDurationUs != C.TIME_UNSET) {
       // Ensure the overridden position doesn't exceed the period duration.
       if (preparePositionOverrideUs >= periodDurationUs) {
diff --git a/library/core/src/test/java/com/google/android/exoplayer2/ExoPlayerTest.java b/library/core/src/test/java/com/google/android/exoplayer2/ExoPlayerTest.java
index dd5df83278..5b17299a53 100644
--- a/library/core/src/test/java/com/google/android/exoplayer2/ExoPlayerTest.java
+++ b/library/core/src/test/java/com/google/android/exoplayer2/ExoPlayerTest.java
@@ -4276,6 +4276,40 @@ public final class ExoPlayerTest {
     assertArrayEquals(new long[] {5_000, 5_000}, currentPlaybackPositions);
   }
 
+  @Test
+  public void
+      timelineUpdateInMultiWindowMediaSource_removingPeriod_withUnpreparedMaskingMediaPeriod_doesNotThrow()
+          throws Exception {
+    TimelineWindowDefinition window1 =
+        new TimelineWindowDefinition(/* periodCount= */ 1, /* id= */ 1);
+    TimelineWindowDefinition window2 =
+        new TimelineWindowDefinition(/* periodCount= */ 1, /* id= */ 2);
+    FakeMediaSource mediaSource = new FakeMediaSource(/* timeline= */ null);
+    ActionSchedule actionSchedule =
+        new ActionSchedule.Builder(TAG)
+            .waitForPlaybackState(Player.STATE_BUFFERING)
+            // Do something and wait so that the player can create its unprepared MaskingMediaPeriod
+            .seek(/* positionMs= */ 0)
+            .waitForSeekProcessed()
+            // Let the player assign the unprepared period to window1.
+            .executeRunnable(() -> mediaSource.setNewSourceInfo(new FakeTimeline(window1, window2)))
+            .waitForTimelineChanged()
+            // Remove window1 and assume the update is handled without throwing.
+            .executeRunnable(() -> mediaSource.setNewSourceInfo(new FakeTimeline(window2)))
+            .waitForTimelineChanged()
+            .stop()
+            .build();
+    new ExoPlayerTestRunner.Builder()
+        .setMediaSources(mediaSource)
+        .setActionSchedule(actionSchedule)
+        .build(context)
+        .start()
+        .blockUntilActionScheduleFinished(TIMEOUT_MS)
+        .blockUntilEnded(TIMEOUT_MS);
+
+    // Assertion is to not throw while running the action schedule above.
+  }
+
   @Test
   public void setPlayWhenReady_keepsCurrentPosition() throws Exception {
     AtomicLong positionAfterSetPlayWhenReady = new AtomicLong(C.TIME_UNSET);