from Jerome Huck Good morning. I did use Gfortran GCC 9.0 on Windows 7 64 bits on an old Fortran77. I attached both the source code and the GCC outputs. I have warning with COMMON. The COMMONS are the same along the code... When compiled I have warnings with different sizes !!! I do not know if it is a bug. I will say it is an issue. There were some bugs/issues in the past see : https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45044 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45045 If you can give me some clues/hints on the subject. Best regards. Jerome Huck.