diff --git a/src/mp4box/trun.rs b/src/mp4box/trun.rs
index efbb2b0..3ca2989 100644
--- a/src/mp4box/trun.rs
+++ b/src/mp4box/trun.rs
@@ -55,6 +55,11 @@ impl TrunBox {
         if TrunBox::FLAG_SAMPLE_CTS & self.flags > 0 {
             sum += 4 * self.sample_count as u64;
         }
+
+        sum += (4 * self.sample_durations.len()) as u64;
+        sum += (4 * self.sample_sizes.len()) as u64;
+        sum += (4 * self.sample_flags.len()) as u64;
+        sum += (4 * self.sample_cts.len()) as u64;
         sum
     }
 }