I've attached an short example code that causes an ICE with the just released 13.1.1 compiler (and presumably earlier). The example includes a variant that doesn't result in an ICE, but which results in what I believe is a spurious fatal code error. The code defines an abstract type and an extension of that type that overrides a deferred function binding. The compiler asserts that the characteristic of the overriding function result differs from the interface of the deferred binding. I don't believe it does. The details, including references to the standard, are in the header of the example.