diff --git a/ProcessLib/GroundwaterFlow.h b/ProcessLib/GroundwaterFlow.h
index 74ea58533844d175e12251ac2985392979243f47..5e62a885cf7fbf3533fb8c387bfc375bf3001d4a 100644
--- a/ProcessLib/GroundwaterFlow.h
+++ b/ProcessLib/GroundwaterFlow.h
@@ -27,7 +27,7 @@ public:
     GroundwaterFlowProcess(MeshLib::Mesh const& mesh,
             std::vector<OGS::ProcessVariable> const& variables,
             ConfigTree const& config)
-        : Process(mesh)
+        : Process(mesh, 1)
     {
         DBUG("Create GroundwaterFlowProcess.");
 
diff --git a/ProcessLib/Process.h b/ProcessLib/Process.h
index ec9596ba7e345fb1f3a5b83c110fd6f7e515070a..aa8c8ecb76a57df28905cdcb99b8ceef76ec5c94 100644
--- a/ProcessLib/Process.h
+++ b/ProcessLib/Process.h
@@ -18,8 +18,8 @@ namespace ProcessLib
 class Process
 {
 public:
-    Process(MeshLib::Mesh const& mesh)
-        : _mesh(mesh)
+    Process(MeshLib::Mesh const& mesh, std::size_t const numberOfNodeVariables)
+        : _mesh(mesh), _numberNodeDOFs(numberOfNodeVariables)
     { }
 
     virtual ~Process() = default;
@@ -28,6 +28,7 @@ public:
 
 protected:
     MeshLib::Mesh const& _mesh;
+    std::size_t const _numberNodeDOFs;
 };
 
 }   // namespace ProcessLib