Hi All, The isfortran function calls a.fnc (Fortran-Not-C), which is implemented as F_CONTIGUOUS && !C_CONTIGUOUS. Before relaxed stride checking contiguous multidimensional arrays could not be both and continguous 1-D arrays were always CONTIGUOUS, but this is not longer the case. Consequently current isfortran breaks backward compatiblity. There are two suggested solutions 1. Return `a.flags.f_contiguous`. This differs for 1-D arrays, but is most consistent with the name isfortran. 2. Return `a.flags.f_contiguous and a.ndim > 1`, which would be backward compatible. It is also possible to start with 2. but add a FutureWarning and later move to 1, which it my preferred solution. See gh-6590 <https://github.com/numpy/numpy/issues/6590> for the issue. Thoughts?