diff --git a/opm/core/simulator/WellState.hpp b/opm/core/simulator/WellState.hpp
index f3bd6274..4f6ea0fb 100644
--- a/opm/core/simulator/WellState.hpp
+++ b/opm/core/simulator/WellState.hpp
@@ -63,6 +63,7 @@ namespace Opm
 
                     // setup wellname -> well index mapping
                     {
+                        assert( wells->name[ w ] );
                         std::string name( wells->name[ w ] );
                         assert( name.size() > 0 );
                         mapentry_t& wellMapEntry = wellMap_[name];