diff --git a/fish-rust/src/flog.rs b/fish-rust/src/flog.rs
index 54550f429..6f6a154c3 100644
--- a/fish-rust/src/flog.rs
+++ b/fish-rust/src/flog.rs
@@ -136,6 +136,28 @@ pub fn all_categories() -> Vec<&'static category_t> {
     );
 }
 
+/// FLOG formats values. By default we would like to use Display, and fall back to Debug.
+/// However that would require specialization. So instead we make two "separate" traits, bring them both in scope,
+/// and let Rust figure it out.
+/// Clients can opt a Debug type into Floggable by implementing FloggableDebug:
+///    impl FloggableDebug for MyType {}
+pub trait FloggableDisplay {
+    /// Return a string representation of this thing.
+    fn to_flog_str(&self) -> String;
+}
+
+impl<T: std::fmt::Display> FloggableDisplay for T {
+    fn to_flog_str(&self) -> String {
+        format!("{}", self)
+    }
+}
+
+pub trait FloggableDebug: std::fmt::Debug {
+    fn to_flog_str(&self) -> String {
+        format!("{:?}", self)
+    }
+}
+
 /// Write to our FLOG file.
 pub fn flog_impl(s: &str) {
     let fd = get_flog_file_fd().0 as RawFd;
@@ -151,9 +173,13 @@ pub fn flog_impl(s: &str) {
 macro_rules! FLOG {
     ($category:ident, $($elem:expr),+) => {
         if crate::flog::categories::$category.enabled.load(std::sync::atomic::Ordering::Relaxed) {
+            #[allow(unused_imports)]
+            use crate::flog::{FloggableDisplay, FloggableDebug};
             let mut vs = Vec::new();
             $(
-                vs.push(format!("{:?}", $elem));
+                {
+                   vs.push($elem.to_flog_str())
+                }
             )+
             // We don't use locking here so we have to append our own newline to avoid multiple writes.
             let mut v = vs.join(" ");
diff --git a/fish-rust/src/threads.rs b/fish-rust/src/threads.rs
index dc4f6419d..579eff682 100644
--- a/fish-rust/src/threads.rs
+++ b/fish-rust/src/threads.rs
@@ -1,9 +1,11 @@
 //! The rusty version of iothreads from the cpp code, to be consumed by native rust code. This isn't
 //! ported directly from the cpp code so we can use rust threads instead of using pthreads.
 
-use crate::flog::FLOG;
+use crate::flog::{FloggableDebug, FLOG};
 use std::thread::{self, ThreadId};
 
+impl FloggableDebug for ThreadId {}
+
 // We don't want to use a full-blown Lazy<T> for the cached main thread id, but we can't use
 // AtomicU64 since std::thread::ThreadId::as_u64() is a nightly-only feature (issue #67939,
 // thread_id_value). We also can't safely transmute `ThreadId` to `NonZeroU64` because there's no
diff --git a/fish-rust/src/topic_monitor.rs b/fish-rust/src/topic_monitor.rs
index 4ef936988..b4dbd291e 100644
--- a/fish-rust/src/topic_monitor.rs
+++ b/fish-rust/src/topic_monitor.rs
@@ -23,7 +23,7 @@
 use crate::fd_readable_set::fd_readable_set_t;
 use crate::fds::{self, autoclose_pipes_t};
 use crate::ffi::{self as ffi, c_int};
-use crate::flog::FLOG;
+use crate::flog::{FloggableDebug, FLOG};
 use crate::wchar::{widestrs, wstr, WString};
 use crate::wchar_ffi::wcharz;
 use nix::errno::Errno;
@@ -79,6 +79,8 @@ pub enum topic_t {
 pub use topic_monitor_ffi::{generation_list_t, topic_t};
 pub type generation_t = u64;
 
+impl FloggableDebug for topic_t {}
+
 /// A generation value which indicates the topic is not of interest.
 pub const invalid_generation: generation_t = std::u64::MAX;