diff --git a/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/DefaultMediaItemConverter.java b/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/DefaultMediaItemConverter.java
index b3a4320a97..dadb1b5251 100644
--- a/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/DefaultMediaItemConverter.java
+++ b/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/DefaultMediaItemConverter.java
@@ -44,7 +44,7 @@ public final class DefaultMediaItemConverter implements MediaItemConverter {
 
   @Override
   public MediaItem toMediaItem(MediaQueueItem item) {
-    return getMediaItem(item.getMedia().getCustomData());
+    return getMediaItem(Assertions.checkNotNull(item.getMedia().getCustomData()));
   }
 
   @Override