diff --git a/MP4/box_mvhd.cpp b/MP4/box_mvhd.cpp
index 0984190e..1592d387 100644
--- a/MP4/box_mvhd.cpp
+++ b/MP4/box_mvhd.cpp
@@ -2,6 +2,8 @@
 
 Box_mvhd::Box_mvhd( ) {
   Container = new Box( 0x6D766864 );
+  SetDefaults();
+  SetReserved();
 }
 
 Box_mvhd::~Box_mvhd() {