diff --git a/opm/core/pressure/IncompTpfa.cpp b/opm/core/pressure/IncompTpfa.cpp
index 62a30b6a8..8a45556fe 100644
--- a/opm/core/pressure/IncompTpfa.cpp
+++ b/opm/core/pressure/IncompTpfa.cpp
@@ -212,7 +212,7 @@ namespace Opm
         // \TODO refactor?
 
         const int nc = grid_.number_of_cells;
-        const int nw = wells_->number_of_wells;
+        const int nw = (wells_) ? wells_->number_of_wells : 0;
 
         // Set up dynamic data.
         computePerSolveDynamicData(dt, state, well_state);