diff --git a/test/visit_each_test.cpp b/test/visit_each_test.cpp
index 726188e..a0da6be 100644
--- a/test/visit_each_test.cpp
+++ b/test/visit_each_test.cpp
@@ -34,7 +34,7 @@ struct V
     {
     }
 
-    template< class T > void operator()( T const & t )
+    template< class T > void operator()( T const & /*t*/ )
     {
     }