Spot the bug in the default-method class

from Interfaces
Java 25 LTS intermediate 4 min 1 issue to find

Find why this class does not compile.

Java
public class Main {
    interface Fast {
        default String mode() { return "fast"; }
    }

    interface Safe {
        default String mode() { return "safe"; }
    }

    static final class Transfer implements Fast, Safe {}
}
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