diff --git a/dune/gfe/rotation.hh b/dune/gfe/rotation.hh
index 222904290259e48f46088521bdb4c8fc885f37f2..eccd772882965f36de83c6862b09e9f48ffda6d7 100644
--- a/dune/gfe/rotation.hh
+++ b/dune/gfe/rotation.hh
@@ -444,6 +444,8 @@ public:
         EmbeddedTangentVector projectedResult = result;
         projectedResult.axpy(-1*(q*result), q);
         
+        assert(std::fabs(projectedResult * q) < 1e-7);
+        
         return projectedResult;
     }