diff --git a/dune/solvers/common/canignore.hh b/dune/solvers/common/canignore.hh
index 019e5f07af72da181cae51998100435d3b4eab48..eb8b4a7fb7cefa4a26043e1e41113994ec6f3bf4 100644
--- a/dune/solvers/common/canignore.hh
+++ b/dune/solvers/common/canignore.hh
@@ -3,6 +3,8 @@
 #ifndef DUNE_SOLVERS_COMMON_CANIGNORE_HH
 #define DUNE_SOLVERS_COMMON_CANIGNORE_HH
 
+#include <cassert>
+
 /** \brief Abstract base class for solvers and iterationsteps that are
  *      able to ignore degrees of freedom described by a bit field.
  */
@@ -59,6 +61,7 @@ public:
      */
     const BitVector& ignore() const
     {
+        assert(hasIgnore());
         return *ignoreNodes_;
     }