https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71014
--- Comment #7 from Keith Lindsay <klindsay at ucar dot edu> --- The Linux system that I'm working on has multiple versions of gcc/gfortran installed. I've compiled and run my example program with different versions and have found the following: Versions 4.9.0, 4.9.1, 4.9.2, 4.9.3, 5.0.1, 5.1.0 Program, as is, works (i.e. no reported mismatches over 10 runs) Versions 5.2.0, 5.3.0, 6.0.1, 6.1.0 Program, as is, reports mismatches (and sometimes hangs) So it seems like the behavior I'm seeing originated in 5.2.0.