Gfortran type mismatch error flag

Gfortran 10 added the default behavior to make type mismatches an error instead of a warning. Legacy Fortran programs too often did not explicitly specify the procedure interfaces to allow implicit polymorphism. The Fortran 2008 standard cleaned up this situation in part with type(*).

Workaround

Gfortran 10 also added flag -fallow-argument-mismatch, which can be used to degrade the errors to warnings. It is however strongly recommended to fix the problem in the legacy code, if it’s part of your code ownership.