diff --git a/opm/autodiff/LinearisedBlackoilResidual.hpp b/opm/autodiff/LinearisedBlackoilResidual.hpp
index acc3e8c83..91fd8478b 100644
--- a/opm/autodiff/LinearisedBlackoilResidual.hpp
+++ b/opm/autodiff/LinearisedBlackoilResidual.hpp
@@ -63,7 +63,7 @@ namespace Opm
         /// pressure specification.
         ADB well_eq;
 
-        std::array<double, 3> matbalscale;
+        std::vector<double> matbalscale;
 
         /// The size of the non-linear system.
         int sizeNonLinear() const;