diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
index 1e7d226c1c..d050c1d37f 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
@@ -734,7 +734,7 @@ public final class DownloadManager {
           break;
         case MSG_CONTENT_LENGTH_CHANGED:
           task = (Task) message.obj;
-          onContentLengthChanged(task);
+          onContentLengthChanged(task, Util.toLong(message.arg1, message.arg2));
           return; // No need to post back to mainHandler.
         case MSG_UPDATE_PROGRESS:
           updateProgress();
@@ -1030,9 +1030,8 @@ public final class DownloadManager {
 
     // Task event processing.
 
-    private void onContentLengthChanged(Task task) {
+    private void onContentLengthChanged(Task task, long contentLength) {
       String downloadId = task.request.id;
-      long contentLength = task.contentLength;
       Download download =
           Assertions.checkNotNull(getDownload(downloadId, /* loadFromIndex= */ false));
       if (contentLength == download.contentLength || contentLength == C.LENGTH_UNSET) {
@@ -1325,7 +1324,13 @@ public final class DownloadManager {
         this.contentLength = contentLength;
         @Nullable Handler internalHandler = this.internalHandler;
         if (internalHandler != null) {
-          internalHandler.obtainMessage(MSG_CONTENT_LENGTH_CHANGED, this).sendToTarget();
+          internalHandler
+              .obtainMessage(
+                  MSG_CONTENT_LENGTH_CHANGED,
+                  (int) (contentLength >> 32),
+                  (int) contentLength,
+                  this)
+              .sendToTarget();
         }
       }
     }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadProgress.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadProgress.java
index 9d946daa28..ba226e60b2 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadProgress.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadProgress.java
@@ -21,8 +21,8 @@ import com.google.android.exoplayer2.C;
 public class DownloadProgress {
 
   /** The number of bytes that have been downloaded. */
-  public long bytesDownloaded;
+  public volatile long bytesDownloaded;
 
   /** The percentage that has been downloaded, or {@link C#PERCENTAGE_UNSET} if unknown. */
-  public float percentDownloaded;
+  public volatile float percentDownloaded;
 }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/Downloader.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/Downloader.java
index fa10d5842b..53485aced6 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/Downloader.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/Downloader.java
@@ -28,6 +28,10 @@ public interface Downloader {
     /**
      * Called when progress is made during a download operation.
      *
+     * <p>May be called directly from {@link #download}, or from any other thread used by the
+     * downloader. In all cases, {@link #download} is guaranteed not to return until after the last
+     * call to {@link #onProgress} has finished executing.
+     *
      * @param contentLength The length of the content in bytes, or {@link C#LENGTH_UNSET} if
      *     unknown.
      * @param bytesDownloaded The number of bytes that have been downloaded.