diff --git a/src/mp4box/traf.rs b/src/mp4box/traf.rs
index 51f812d..95e6f6e 100644
--- a/src/mp4box/traf.rs
+++ b/src/mp4box/traf.rs
@@ -104,6 +104,12 @@ impl<W: Write> WriteBox<&mut W> for TrafBox {
         BoxHeader::new(self.box_type(), size).write(writer)?;
 
         self.tfhd.write_box(writer)?;
+        if let Some(ref tfdt) = self.tfdt {
+            tfdt.write_box(writer)?;
+        }
+        if let Some(ref trun) = self.trun {
+            trun.write_box(writer)?;
+        }
 
         Ok(size)
     }