rust/src/librustc_error_codes/error_codes/E0326.md

The types of any associated constants in a trait implementation must match the types in the trait definition. This error indicates that there was a mismatch.

Here's an example of this error:

trait Foo {
    const BAR: bool;
}

struct Bar;

impl Foo for Bar {
    const BAR: u32 = 5; // error, expected bool, found u32
}