diff --git a/mjpegtools/y4mdenoise/Region2D.hh b/mjpegtools/y4mdenoise/Region2D.hh
index 536e23e..7414d4e 100644
--- a/mjpegtools/y4mdenoise/Region2D.hh
+++ b/mjpegtools/y4mdenoise/Region2D.hh
@@ -16,7 +16,7 @@ #define __REGION2D_H__
 
 #include "Status_t.h"
 #include <iostream>
-
+#include <assert.h>
 
 
 // The 2-dimensional region class.  Parameterized by the numeric type