fst: Thread panics on read operations of FST set file

I’m seeing a very small percentage of “corrupt” FST set files that are triggering panics in Rust (leading to a Python interpreter segfault). The errors look like:

thread '<unnamed>' panicked at 'index out of bounds: the len is 17498006 but the index is 15336395951936096993', /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/fst-0.3.0/src/raw/node.rs:306:17

thread '<unnamed>' panicked at 'index out of bounds: the len is 89225255 but the index is 15119944950614189002', /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/fst-0.3.0/src/raw/node.rs:306:17

thread '<unnamed>' panicked at 'index out of bounds: the len is 16285338 but the index is 3532794445444415790', /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/fst-0.3.0/src/raw/node.rs:306:17                      

This occurs on approximately 13 out of 4635 files, ranging in size from 20MB to > 100MB. I have not been able to narrow things down past this, but wanted to know what might cause this?

I’m shelling out to the fst-bin crate to combine multiple input files into larger files, then doing set operations on the merged output. The fst binary was built on Rust nightly; I’m not sure of the exact version at the moment.