diff --git a/opm/simulators/flow/CompositionalContainer.hpp b/opm/simulators/flow/CompositionalContainer.hpp
index 9afb7eee8..f2b2a2a2f 100644
--- a/opm/simulators/flow/CompositionalContainer.hpp
+++ b/opm/simulators/flow/CompositionalContainer.hpp
@@ -69,6 +69,7 @@ public:
     bool allocated() const
     { return allocated_; }
 
+private:
     bool allocated_ = false;
     // total mole fractions for each component
     std::array<ScalarBuffer, numComponents> moleFractions_;