diff --git a/src/NIS/NIS_Surface.cxx b/src/NIS/NIS_Surface.cxx
index b59eb0071d..c51e3ba370 100755
--- a/src/NIS/NIS_Surface.cxx
+++ b/src/NIS/NIS_Surface.cxx
@@ -486,7 +486,7 @@ void  NIS_Surface::SetDisplayMode (const NIS_Surface::DisplayMode theMode)
       isUpdate = Standard_True;
     }
   }
-  if (isUpdate && GetDrawer()) {
+  if (isUpdate && !GetDrawer().IsNull()) {
     const Handle(NIS_SurfaceDrawer) aDrawer =
       static_cast<NIS_SurfaceDrawer *>(DefaultDrawer(0L));
     aDrawer->Assign (GetDrawer());
diff --git a/src/ViewerTest/ViewerTest_ViewerCommands.cxx b/src/ViewerTest/ViewerTest_ViewerCommands.cxx
index 9f0996999e..d634c029ad 100755
--- a/src/ViewerTest/ViewerTest_ViewerCommands.cxx
+++ b/src/ViewerTest/ViewerTest_ViewerCommands.cxx
@@ -2425,7 +2425,7 @@ V3d_LineItem::V3d_LineItem(Standard_Real X1, Standard_Real Y1,
   myX1(X1), myY1(Y1), myX2(X2), myY2(Y2), myLayerMgr(theLayerMgr),
   myType(theType), myWidth(theWidth), myTransparency(theTransp)
 {
-  if (myLayerMgr && myLayerMgr->Overlay())
+  if (myLayerMgr && !myLayerMgr->Overlay().IsNull())
     myLayerMgr->Overlay()->AddLayerItem (this);
 }