https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66153 Grid code breaks on GCC4.8, 4.9, 5.0 due to the peekIndex operating on lattice. It erroneously recurses back into the Lattice variant, even though the lattice container is dropped. Work around is possible; if the Lattice routine is given a disambiguating name prefix, such as latPeekIndex GCC5 works. However this is ugly and for now I have submitted a bug report to see the reaction and speed of fixing. The simple testcase in this directory is the submitted bug report that encapsulates the problem. The test case works with icpc and with clang++, but fails consistently on g++ current variants. Peter