diff --git a/Code/IO/otbDEMHandler.cxx b/Code/IO/otbDEMHandler.cxx
index 870c1e05761fa8e851013f5833fb429a025a79ea..c589fd4398b9169009d3cdb1f0fa508ac2c1aa18 100644
--- a/Code/IO/otbDEMHandler.cxx
+++ b/Code/IO/otbDEMHandler.cxx
@@ -86,9 +86,9 @@ DEMHandler
   ossimGpt ossimWorldPoint;
   ossimWorldPoint.lon=geoPoint[0];
   ossimWorldPoint.lat=geoPoint[1];
-//   m_Mutex.Lock();
+  m_Mutex.Lock();
   height=m_ElevManager->getHeightAboveMSL(ossimWorldPoint);
-//   m_Mutex.Unlock();
+  m_Mutex.Unlock();
   return height;
 }