We had a testfailure in sequoia on s390x in Debian, and this reproduces the error.

Test output:

363s failures:
363s
363s ---- packet::test::mutate_eq_discriminates stdout ----
363s thread 'packet::test::mutate_eq_discriminates' panicked at '[quickcheck] TEST FAILED. Arguments: (-----BEGIN PGP ARMORED FILE-----
363s
363s w8BRBU4CAuyZ1F8AIADMWALvqVxDf787kQH3ZhXdebbRpneHZjl7+KlY2wfTVEad
363s 7wAJB43JggBr6F9Yprbu48JX+xFAFkXbhh/AWD1W7qQXlKIz4HDd3BBE2QNfzKVN
363s GQtfXs4AdI53W1L/KibaFcT0cwD8ANn/wtxjP6FO+2eGvRoc6wG+ogDwa8FlrAFy
363s hoH9r0Bu3zoXex0jBmRtgN8HXj4A/05z76OfuCyZhgHC/9/8AU+6hyTUYOzyVPES
363s uYttawHWpFxW/i9zAUmk0P8ZyRE+/8CCGr8wyscORUuCVrCjjWzSlEpDnh1aNJIY
363s /99JYLLapQcL2G7BkCrSKQsB5NkJ+Nb/6JpiAAE+aVYARRal
363s =49fD
363s -----END PGP ARMORED FILE-----
363s , 1863593116114256088)', /usr/share/cargo/registry/quickcheck-1.0.3/src/tester.rs:165:28
363s stack backtrace:
363s    0: std::panicking::begin_panic
363s              at /usr/src/rustc-1.70.0/library/std/src/panicking.rs:610:12
363s    1: quickcheck::tester::QuickCheck::quickcheck
363s              at /usr/share/cargo/registry/quickcheck-1.0.3/src/tester.rs:165:28
363s    2: quickcheck::tester::quickcheck
363s              at /usr/share/cargo/registry/quickcheck-1.0.3/src/tester.rs:183:5
363s    3: sequoia_openpgp::packet::test::mutate_eq_discriminates
363s              at /usr/share/cargo/registry/quickcheck-1.0.3/src/lib.rs:62:21
363s    4: sequoia_openpgp::packet::test::mutate_eq_discriminates::{{closure}}
363s              at /usr/share/cargo/registry/quickcheck-1.0.3/src/lib.rs:58:31
363s    5: core::ops::function::FnOnce::call_once
363s              at /usr/src/rustc-1.70.0/library/core/src/ops/function.rs:250:5
363s    6: core::ops::function::FnOnce::call_once
363s              at /usr/src/rustc-1.70.0/library/core/src/ops/function.rs:250:5
363s note: Some details are omitted, run with  for a verbose backtrace.
363s
363s
363s failures:
363s     packet::test::mutate_eq_discriminates
363s

1 files changed, 36 insertions, 0 deletions

diff --git a/openpgp/src/packet/mod.rs b/openpgp/src/packet/mod.rs
index 3a773a3a..4837b26a 100644
--- a/openpgp/src/packet/mod.rs
+++ b/openpgp/src/packet/mod.rs
@@ -2068,6 +2068,42 @@ mod test {
     }
 
     /// Problem on systems with 32-bit time_t.
+    #[cfg(target_pointer_width = "64")]
+    #[test]
+    fn issue_XXX() {
+        let p = Packet::from_bytes(b"-----BEGIN PGP ARMORED FILE-----
+
+w8BRBU4CAuyZ1F8AIADMWALvqVxDf787kQH3ZhXdebbRpneHZjl7+KlY2wfTVEad
+7wAJB43JggBr6F9Yprbu48JX+xFAFkXbhh/AWD1W7qQXlKIz4HDd3BBE2QNfzKVN
+GQtfXs4AdI53W1L/KibaFcT0cwD8ANn/wtxjP6FO+2eGvRoc6wG+ogDwa8FlrAFy
+hoH9r0Bu3zoXex0jBmRtgN8HXj4A/05z76OfuCyZhgHC/9/8AU+6hyTUYOzyVPES
+uYttawHWpFxW/i9zAUmk0P8ZyRE+/8CCGr8wyscORUuCVrCjjWzSlEpDnh1aNJIY
+/99JYLLapQcL2G7BkCrSKQsB5NkJ+Nb/6JpiAAE+aVYARRal
+=49fD
+-----END PGP ARMORED FILE-----
+").unwrap();
+
+        if p.tag() == Tag::CompressedData {
+            // Mutating compressed data streams is not that
+            // trivial, because there are bits we can flip without
+            // changing the decompressed data.
+            return;
+        }
+
+        let mut buf = p.to_vec().unwrap();
+        eprintln!("bit = {}", bit);
+        buf[bit / 8] ^= 1 << (bit % 8);
+
+        assert_eq!(true,
+            match Packet::from_bytes(&buf) {
+                Ok(q) => p != q,
+                Err(_) => true, // Packet failed to parse.
+            }
+        );
+    }
+
+
+    /// Problem on systems with 32-bit time_t.
     #[test]
     fn issue_802() -> Result<()> {
         let pp = crate::PacketPile::from_bytes(b"-----BEGIN PGP ARMORED FILE-----