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 1049d266f9..e28c1652f2 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
@@ -141,6 +141,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
   @Override
   protected synchronized void onChildSourceInfoRefreshed(
       Void id, MediaSource mediaSource, Timeline newTimeline) {
+    @Nullable MediaPeriodId idForMaskingPeriodPreparation = null;
     if (isPrepared) {
       timeline = timeline.cloneWithUpdatedTimeline(newTimeline);
     } else if (newTimeline.isEmpty()) {
@@ -183,14 +184,17 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
       if (unpreparedMaskingMediaPeriod != null) {
         MaskingMediaPeriod maskingPeriod = unpreparedMaskingMediaPeriod;
         maskingPeriod.overridePreparePositionUs(periodPositionUs);
-        MediaPeriodId idInSource =
+        idForMaskingPeriodPreparation =
             maskingPeriod.id.copyWithPeriodUid(getInternalPeriodUid(maskingPeriod.id.periodUid));
-        maskingPeriod.createPeriod(idInSource);
       }
     }
     hasRealTimeline = true;
     isPrepared = true;
     refreshSourceInfo(this.timeline);
+    if (idForMaskingPeriodPreparation != null) {
+      Assertions.checkNotNull(unpreparedMaskingMediaPeriod)
+          .createPeriod(idForMaskingPeriodPreparation);
+    }
   }
 
   @Nullable
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 ca772f85e2..602cff4391 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
@@ -2988,7 +2988,7 @@ public final class ExoPlayerTest {
                 /* isDynamic= */ false,
                 /* durationUs= */ 10_000_000,
                 adPlaybackState));
-    final FakeMediaSource fakeMediaSource = new FakeMediaSource(fakeTimeline);
+    FakeMediaSource fakeMediaSource = new FakeMediaSource(/* timeline= */ null);
     AtomicReference<Player> playerReference = new AtomicReference<>();
     AtomicLong contentStartPositionMs = new AtomicLong(C.TIME_UNSET);
     EventListener eventListener =
@@ -3011,6 +3011,59 @@ public final class ExoPlayerTest {
                   }
                 })
             .seek(/* positionMs= */ 5_000)
+            .waitForPlaybackState(Player.STATE_BUFFERING)
+            .executeRunnable(() -> fakeMediaSource.setNewSourceInfo(fakeTimeline))
+            .build();
+    new ExoPlayerTestRunner.Builder()
+        .setMediaSources(fakeMediaSource)
+        .setActionSchedule(actionSchedule)
+        .build(context)
+        .start()
+        .blockUntilEnded(TIMEOUT_MS);
+
+    assertThat(contentStartPositionMs.get()).isAtLeast(5_000L);
+  }
+
+  @Test
+  public void contentWithoutInitialSeekStartsAtDefaultPositionAfterPrerollAd() throws Exception {
+    AdPlaybackState adPlaybackState =
+        FakeTimeline.createAdPlaybackState(/* adsPerAdGroup= */ 3, /* adGroupTimesUs...= */ 0);
+    Timeline fakeTimeline =
+        new FakeTimeline(
+            new TimelineWindowDefinition(
+                /* periodCount= */ 1,
+                /* id= */ 0,
+                /* isSeekable= */ true,
+                /* isDynamic= */ false,
+                /* isLive= */ false,
+                /* isPlaceholder= */ false,
+                /* durationUs= */ 10_000_000,
+                /* defaultPositionUs= */ 5_000_000,
+                adPlaybackState));
+    FakeMediaSource fakeMediaSource = new FakeMediaSource(/* timeline= */ null);
+    AtomicReference<Player> playerReference = new AtomicReference<>();
+    AtomicLong contentStartPositionMs = new AtomicLong(C.TIME_UNSET);
+    EventListener eventListener =
+        new EventListener() {
+          @Override
+          public void onPositionDiscontinuity(@DiscontinuityReason int reason) {
+            if (reason == Player.DISCONTINUITY_REASON_AD_INSERTION) {
+              contentStartPositionMs.set(playerReference.get().getContentPosition());
+            }
+          }
+        };
+    ActionSchedule actionSchedule =
+        new ActionSchedule.Builder("contentWithoutInitialSeekStartsAtDefaultPositionAfterPrerollAd")
+            .executeRunnable(
+                new PlayerRunnable() {
+                  @Override
+                  public void run(SimpleExoPlayer player) {
+                    playerReference.set(player);
+                    player.addListener(eventListener);
+                  }
+                })
+            .waitForPlaybackState(Player.STATE_BUFFERING)
+            .executeRunnable(() -> fakeMediaSource.setNewSourceInfo(fakeTimeline))
             .build();
     new ExoPlayerTestRunner.Builder()
         .setMediaSources(fakeMediaSource)
diff --git a/testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeTimeline.java b/testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeTimeline.java
index 5b882dd9a5..628d7b191d 100644
--- a/testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeTimeline.java
+++ b/testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeTimeline.java
@@ -42,6 +42,7 @@ public final class FakeTimeline extends Timeline {
     public final boolean isLive;
     public final boolean isPlaceholder;
     public final long durationUs;
+    public final long defaultPositionUs;
     public final AdPlaybackState adPlaybackState;
 
     /**
@@ -59,6 +60,7 @@ public final class FakeTimeline extends Timeline {
           /* isLive= */ false,
           /* isPlaceholder= */ true,
           /* durationUs= */ C.TIME_UNSET,
+          /* defaultPositionUs= */ 0,
           AdPlaybackState.NONE);
     }
 
@@ -126,6 +128,7 @@ public final class FakeTimeline extends Timeline {
           /* isLive= */ isDynamic,
           /* isPlaceholder= */ false,
           durationUs,
+          /* defaultPositionUs= */ 0,
           adPlaybackState);
     }
 
@@ -140,6 +143,7 @@ public final class FakeTimeline extends Timeline {
      * @param isLive Whether the window is live.
      * @param isPlaceholder Whether the window is a placeholder.
      * @param durationUs The duration of the window in microseconds.
+     * @param defaultPositionUs The default position of the window in microseconds.
      * @param adPlaybackState The ad playback state.
      */
     public TimelineWindowDefinition(
@@ -150,6 +154,7 @@ public final class FakeTimeline extends Timeline {
         boolean isLive,
         boolean isPlaceholder,
         long durationUs,
+        long defaultPositionUs,
         AdPlaybackState adPlaybackState) {
       this.periodCount = periodCount;
       this.id = id;
@@ -158,6 +163,7 @@ public final class FakeTimeline extends Timeline {
       this.isLive = isLive;
       this.isPlaceholder = isPlaceholder;
       this.durationUs = durationUs;
+      this.defaultPositionUs = defaultPositionUs;
       this.adPlaybackState = adPlaybackState;
     }
   }
@@ -252,7 +258,7 @@ public final class FakeTimeline extends Timeline {
         windowDefinition.isSeekable,
         windowDefinition.isDynamic,
         windowDefinition.isLive,
-        /* defaultPositionUs= */ 0,
+        windowDefinition.defaultPositionUs,
         windowDefinition.durationUs,
         periodOffsets[windowIndex],
         periodOffsets[windowIndex + 1] - 1,