diff --git a/dumux/common/boundaryflag.hh b/dumux/common/boundaryflag.hh
index c095bf3024d4bd45dc3003332e87d2ecae435e5a..29dae7b4456d88a578439c5406a664d732840234 100644
--- a/dumux/common/boundaryflag.hh
+++ b/dumux/common/boundaryflag.hh
@@ -67,7 +67,7 @@ public:
     BoundaryFlag(const Intersection& i) : flag_(-1)
     {
         if (i.boundary())
-            flag_ = i.boundaryId();
+            flag_ = i.impl().boundaryId();
     }
 
     using value_type = int;