`h1` will fail on 32-bit targets if a hasher yields a `u64` greater than `u32::MAX`: https://github.com/Amanieu/hashbrown/blob/9068eb7a2268d879dc4453ac72238e8a992f1469/src/raw/mod.rs#L120-L126 The comment in `h2` gives some insight to this, but that **only** applies to `FxHash`: https://github.com/Amanieu/hashbrown/blob/9068eb7a2268d879dc4453ac72238e8a992f1469/src/raw/mod.rs#L131-L138 See also the failure in https://github.com/rust-lang/rust/pull/58623#issuecomment-482373125