diff --git a/src/foam/matrices/lduMatrix/lduAddressing/lduInterfaces/lduInterface/lduInterface.C b/src/foam/matrices/lduMatrix/lduAddressing/lduInterfaces/lduInterface/lduInterface.C
index ac309dbba..11e870e9a 100644
--- a/src/foam/matrices/lduMatrix/lduAddressing/lduInterfaces/lduInterface/lduInterface.C
+++ b/src/foam/matrices/lduMatrix/lduAddressing/lduInterfaces/lduInterface/lduInterface.C
@@ -59,7 +59,7 @@ Foam::autoPtr<Foam::crMatrix> Foam::lduInterface::prolongationTransfer
     );
 
     // Dummy return to make the compiler happy
-    return autoPtr<crMatrix>(NULL);
+    return autoPtr<crMatrix>(nullptr);
 }