diff --git a/library/core/src/main/java/com/google/android/exoplayer2/upstream/DataSource.java b/library/core/src/main/java/com/google/android/exoplayer2/upstream/DataSource.java
index b3bb34e34f..c759499577 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/upstream/DataSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/upstream/DataSource.java
@@ -44,9 +44,7 @@ public interface DataSource {
    *
    * @param transferListener A {@link TransferListener}.
    */
-  default void addTransferListener(TransferListener transferListener) {
-    // TODO: Make non-default once all DataSources implement this method.
-  }
+  void addTransferListener(TransferListener transferListener);
 
   /**
    * Opens the source to read the specified data.
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/upstream/DummyDataSource.java b/library/core/src/main/java/com/google/android/exoplayer2/upstream/DummyDataSource.java
index fa3e14f1c9..06dc79e345 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/upstream/DummyDataSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/upstream/DummyDataSource.java
@@ -16,6 +16,7 @@
 package com.google.android.exoplayer2.upstream;
 
 import android.net.Uri;
+import android.support.annotation.Nullable;
 import java.io.IOException;
 
 /**
@@ -35,6 +36,11 @@ public final class DummyDataSource implements DataSource {
 
   private DummyDataSource() {}
 
+  @Override
+  public void addTransferListener(TransferListener transferListener) {
+    // Do nothing.
+  }
+
   @Override
   public long open(DataSpec dataSpec) throws IOException {
     throw new IOException("Dummy source");
@@ -46,7 +52,7 @@ public final class DummyDataSource implements DataSource {
   }
 
   @Override
-  public Uri getUri() {
+  public @Nullable Uri getUri() {
     return null;
   }
 
@@ -54,5 +60,4 @@ public final class DummyDataSource implements DataSource {
   public void close() throws IOException {
     // do nothing.
   }
-
 }
diff --git a/library/hls/src/test/java/com/google/android/exoplayer2/source/hls/Aes128DataSourceTest.java b/library/hls/src/test/java/com/google/android/exoplayer2/source/hls/Aes128DataSourceTest.java
index 86bffc7762..93f724e630 100644
--- a/library/hls/src/test/java/com/google/android/exoplayer2/source/hls/Aes128DataSourceTest.java
+++ b/library/hls/src/test/java/com/google/android/exoplayer2/source/hls/Aes128DataSourceTest.java
@@ -21,6 +21,7 @@ import android.net.Uri;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.upstream.DataSource;
 import com.google.android.exoplayer2.upstream.DataSpec;
+import com.google.android.exoplayer2.upstream.TransferListener;
 import java.io.IOException;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -76,6 +77,9 @@ public class Aes128DataSourceTest {
     public boolean opened;
     public boolean closedCalled;
 
+    @Override
+    public void addTransferListener(TransferListener transferListener) {}
+
     @Override
     public long open(DataSpec dataSpec) throws IOException {
       opened = true;