error: 'constexpr' does not name a type

When building opm-porsol (release/2013.03 branch) on rhel 5 I get the following error:

/private/laods/opm/RH5/realization_cmake/only_cmake/opm-porsol/opm/porsol/blackoil/co2fluid/opm/material/constants.hh:46: error: 'constexpr' does not name a type

Can this be a compilator error? I use gcc 4.1.2.