diff --git a/opm/autodiff/WellStateFullyImplicitBlackoil.hpp b/opm/autodiff/WellStateFullyImplicitBlackoil.hpp
index 8f8a130cb..c2aa6e828 100644
--- a/opm/autodiff/WellStateFullyImplicitBlackoil.hpp
+++ b/opm/autodiff/WellStateFullyImplicitBlackoil.hpp
@@ -280,6 +280,7 @@ namespace Opm
             {
                 // we need to create a trival segment related values to avoid there will be some
                 // multi-segment wells added later.
+                nseg_ = nw;
                 top_segment_index_.reserve(nw);
                 for (int w = 0; w < nw; ++w) {
                     top_segment_index_.push_back(w);