diff --git a/tests/pde/MGTest.cpp b/tests/pde/MGTest.cpp
index 275a2ecc19150c0300dd96927c9254ddfd9f2da9..9993de251d27260773698b8f9645bd15348d4b8c 100644
--- a/tests/pde/MGTest.cpp
+++ b/tests/pde/MGTest.cpp
@@ -71,6 +71,7 @@ void initU( const shared_ptr< StructuredBlockStorage > & blocks, const BlockData
          sum += u->get( *cell );
       }
    }
+   WALBERLA_UNUSED(sum);
 }