diff --git a/mm-server/src/compositor.rs b/mm-server/src/compositor.rs
index 7e3db61..c3f1555 100644
--- a/mm-server/src/compositor.rs
+++ b/mm-server/src/compositor.rs
@@ -22,6 +22,7 @@ mod video;
 mod xwayland;
 
 use std::{
+    collections::BTreeMap,
     ffi::{OsStr, OsString},
     fs::File,
     io::{BufRead, BufReader},
@@ -36,7 +37,6 @@ use child::*;
 pub use control::*;
 use crossbeam_channel as crossbeam;
 pub use handle::*;
-use hashbrown::HashMap;
 pub use input::GamepadLayout;
 use lazy_static::lazy_static;
 use protocols::*;
@@ -121,7 +121,7 @@ pub struct State {
 
     default_seat: seat::Seat,
     input_manager: input::InputDeviceManager,
-    gamepads: HashMap<u64, input::GamepadHandle>,
+    gamepads: BTreeMap<u64, input::GamepadHandle>,
 
     app_config: AppConfig,
     display_params: DisplayParams,
@@ -138,7 +138,7 @@ pub struct State {
     audio_pipeline: audio::EncodePipeline,
 
     xwm: Option<xwayland::Xwm>,
-    xwayland_surface_lookup: HashMap<u64, surface::SurfaceKey>,
+    xwayland_surface_lookup: BTreeMap<u64, surface::SurfaceKey>,
 
     // At the bottom for drop order.
     vk: Arc<VkContext>,
@@ -226,7 +226,7 @@ impl Compositor {
 
         // Set up input emulation (this is just for gamepads).
         let mut input_manager = input::InputDeviceManager::new(&mut container)?;
-        let mut gamepads = HashMap::new();
+        let mut gamepads = BTreeMap::new();
 
         for (pad_id, layout) in permanent_gamepads {
             let dev = input_manager.plug_gamepad(pad_id, layout, true)?;
@@ -265,7 +265,7 @@ impl Compositor {
             audio_pipeline,
 
             xwm: None,
-            xwayland_surface_lookup: HashMap::default(),
+            xwayland_surface_lookup: BTreeMap::default(),
 
             vk,
         };
@@ -1007,19 +1007,17 @@ impl Compositor {
                 self.state.default_seat.lift_pointer(&self.state.serial);
             }
             ControlMessage::GamepadAvailable(id) => {
-                if !self.state.gamepads.contains_key(&id) {
-                    self.state.gamepads.insert(
+                use std::collections::btree_map::Entry;
+                if let Entry::Vacant(e) = self.state.gamepads.entry(id) {
+                    e.insert(self.state.input_manager.plug_gamepad(
                         id,
-                        self.state.input_manager.plug_gamepad(
-                            id,
-                            input::GamepadLayout::GenericDualStick,
-                            false,
-                        )?,
-                    );
+                        input::GamepadLayout::GenericDualStick,
+                        false,
+                    )?);
                 }
             }
             ControlMessage::GamepadUnavailable(id) => {
-                use hashbrown::hash_map::Entry;
+                use std::collections::btree_map::Entry;
                 match self.state.gamepads.entry(id) {
                     Entry::Occupied(v) if !v.get().permanent => {
                         v.remove();
diff --git a/mm-server/src/compositor/audio/pulse.rs b/mm-server/src/compositor/audio/pulse.rs
index fa2f0a6..ad6ef3e 100644
--- a/mm-server/src/compositor/audio/pulse.rs
+++ b/mm-server/src/compositor/audio/pulse.rs
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: BUSL-1.1
 
 use std::{
-    collections::VecDeque,
+    collections::{BTreeMap, VecDeque},
     ffi::{CStr, CString},
     io::{prelude::*, Cursor},
     path::Path,
@@ -15,7 +15,6 @@ use anyhow::{bail, Context};
 use bytes::BytesMut;
 use crossbeam_channel as crossbeam;
 use cstr::cstr;
-use hashbrown::HashMap;
 use mio::net::UnixListener;
 use pulseaudio::protocol::{self as pulse, ClientInfoList};
 use tracing::{debug, error, trace, warn};
@@ -62,7 +61,7 @@ struct Client {
     protocol_version: u16,
     props: Option<pulse::Props>,
     incoming: BytesMut,
-    playback_streams: HashMap<u32, PlaybackStream>,
+    playback_streams: BTreeMap<u32, PlaybackStream>,
 }
 
 struct ServerState {
@@ -82,7 +81,7 @@ pub struct PulseServer {
     unencoded_tx: crossbeam::Sender<EncodeFrame>,
     done_rx: crossbeam::Receiver<EncodeFrame>,
 
-    clients: HashMap<mio::Token, Client>,
+    clients: BTreeMap<mio::Token, Client>,
     server_state: ServerState,
 }
 
@@ -188,7 +187,7 @@ impl PulseServer {
                 unencoded_tx,
                 done_rx,
                 close_rx,
-                clients: HashMap::new(),
+                clients: BTreeMap::new(),
                 server_state: ServerState {
                     server_info,
                     cards: vec![], // vec![dummy_card],
@@ -258,7 +257,7 @@ impl PulseServer {
                                 protocol_version: pulse::MAX_VERSION,
                                 props: None,
                                 incoming: BytesMut::new(),
-                                playback_streams: HashMap::new(),
+                                playback_streams: BTreeMap::new(),
                             },
                         );
                     }
diff --git a/mm-server/src/compositor/child/container.rs b/mm-server/src/compositor/child/container.rs
index 16f6e60..10b46e2 100644
--- a/mm-server/src/compositor/child/container.rs
+++ b/mm-server/src/compositor/child/container.rs
@@ -825,7 +825,7 @@ fn sync_barrier(barrier: &ipc::EventfdBarrier) -> rustix::io::Result<()> {
 
 #[cfg(test)]
 mod test {
-    use std::{collections::HashMap, fs::File, io::Read as _};
+    use std::{fs::File, io::Read as _};
 
     use rustix::pipe::{pipe_with, PipeFlags};
 
@@ -839,7 +839,7 @@ mod test {
         let app_config = AppConfig {
             description: None,
             command: vec!["echo".to_owned().into(), "done".to_owned().into()],
-            env: HashMap::new(),
+            env: Default::default(),
             xwayland: false,
             force_1x_scale: false,
             home_isolation_mode: HomeIsolationMode::Unisolated,
diff --git a/mm-server/src/compositor/handle.rs b/mm-server/src/compositor/handle.rs
index 4ec0fac..87b5f9d 100644
--- a/mm-server/src/compositor/handle.rs
+++ b/mm-server/src/compositor/handle.rs
@@ -2,16 +2,18 @@
 //
 // SPDX-License-Identifier: BUSL-1.1
 
-use std::sync::{Arc, RwLock};
+use std::{
+    collections::BTreeMap,
+    sync::{Arc, RwLock},
+};
 
 use crossbeam_channel as crossbeam;
-use hashbrown::HashMap;
 
 use super::CompositorEvent;
 
 #[derive(Debug, Clone)]
 struct Inner {
-    attachments: HashMap<u64, crossbeam::Sender<CompositorEvent>>,
+    attachments: BTreeMap<u64, crossbeam::Sender<CompositorEvent>>,
 }
 
 #[derive(Debug, Clone)]
@@ -21,7 +23,7 @@ impl CompositorHandle {
     pub fn new(waker: Arc<mio::Waker>) -> Self {
         Self(
             Arc::new(RwLock::new(Inner {
-                attachments: HashMap::new(),
+                attachments: BTreeMap::new(),
             })),
             waker,
         )
@@ -52,7 +54,7 @@ impl CompositorHandle {
 
     pub fn kick_clients(&self) {
         let attachments = &mut self.0.write().unwrap().attachments;
-        for (_, sender) in attachments.drain() {
+        for (_, sender) in std::mem::take(attachments) {
             sender.send(CompositorEvent::Shutdown).ok();
         }
     }
diff --git a/mm-server/src/compositor/input.rs b/mm-server/src/compositor/input.rs
index 9af2549..2ecce0a 100644
--- a/mm-server/src/compositor/input.rs
+++ b/mm-server/src/compositor/input.rs
@@ -232,7 +232,7 @@ impl InputDeviceManager {
 
 #[cfg(test)]
 mod test {
-    use std::{collections::HashMap, fs::File, io::Read as _};
+    use std::{fs::File, io::Read as _};
 
     use rustix::pipe::{pipe_with, PipeFlags};
 
@@ -255,7 +255,7 @@ mod test {
         let app_config = AppConfig {
             description: None,
             command,
-            env: HashMap::new(),
+            env: Default::default(),
             xwayland: false,
             force_1x_scale: false,
             home_isolation_mode: HomeIsolationMode::Unisolated,
diff --git a/mm-server/src/compositor/input/udevfs.rs b/mm-server/src/compositor/input/udevfs.rs
index 794f5b0..9996abe 100644
--- a/mm-server/src/compositor/input/udevfs.rs
+++ b/mm-server/src/compositor/input/udevfs.rs
@@ -2,7 +2,7 @@
 //
 // SPDX-License-Identifier: BUSL-1.1
 
-use std::{collections::HashMap, path::PathBuf, str::FromStr as _, sync::Arc, time};
+use std::{collections::BTreeMap, path::PathBuf, str::FromStr as _, sync::Arc, time};
 
 use fuser as fuse;
 use libc::EBADF;
@@ -125,14 +125,14 @@ impl TryFrom<u64> for DeviceInode {
 ///     device.
 pub struct UdevFs {
     state: Arc<Mutex<super::InputManagerState>>,
-    static_inodes: HashMap<u64, StaticEntry>, // Indexed by inode.
+    static_inodes: BTreeMap<u64, StaticEntry>, // Indexed by inode.
 }
 
 impl UdevFs {
     pub fn new(state: Arc<Mutex<super::InputManagerState>>) -> Self {
         let ctime = time::SystemTime::now();
 
-        let mut static_inodes: HashMap<u64, StaticEntry> = HashMap::new();
+        let mut static_inodes: BTreeMap<u64, StaticEntry> = BTreeMap::new();
 
         for (idx, entry) in STATIC_DIRS.iter().enumerate() {
             let mut relpath = PathBuf::from_str(entry).unwrap();
diff --git a/mm-server/src/compositor/video/vulkan_encode/dpb.rs b/mm-server/src/compositor/video/vulkan_encode/dpb.rs
index 3b3803c..ed479dd 100644
--- a/mm-server/src/compositor/video/vulkan_encode/dpb.rs
+++ b/mm-server/src/compositor/video/vulkan_encode/dpb.rs
@@ -2,10 +2,9 @@
 //
 // SPDX-License-Identifier: BUSL-1.1
 
-use std::sync::Arc;
+use std::{collections::BTreeMap, sync::Arc};
 
 use ash::vk;
-use hashbrown::HashMap;
 
 use crate::vulkan::*;
 
@@ -22,7 +21,7 @@ pub struct DpbPicture {
 pub struct DpbPool {
     _store: Vec<VkImage>,
     slots: Vec<DpbPicture>,
-    ids: HashMap<u32, usize>,
+    ids: BTreeMap<u32, usize>,
 }
 
 impl DpbPool {
@@ -58,7 +57,7 @@ impl DpbPool {
         Ok(Self {
             _store: vec![image],
             slots,
-            ids: HashMap::new(),
+            ids: BTreeMap::new(),
         })
     }
 
@@ -93,7 +92,7 @@ impl DpbPool {
         Ok(Self {
             _store: store,
             slots,
-            ids: HashMap::new(),
+            ids: BTreeMap::new(),
         })
     }
 
diff --git a/mm-server/src/compositor/xwayland/xwm.rs b/mm-server/src/compositor/xwayland/xwm.rs
index cc41e73..be68530 100644
--- a/mm-server/src/compositor/xwayland/xwm.rs
+++ b/mm-server/src/compositor/xwayland/xwm.rs
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: BUSL-1.1
 
 use std::{
-    collections::HashMap,
+    collections::BTreeMap,
     os::fd::{AsFd as _, BorrowedFd},
 };
 
@@ -116,8 +116,8 @@ pub struct Xwm {
     client_list: Vec<u32>,
     client_list_stacking: Vec<u32>,
 
-    pub xwindows: HashMap<u32, XWindow>,
-    pub serials: HashMap<u64, u32>,
+    pub xwindows: BTreeMap<u32, XWindow>,
+    pub serials: BTreeMap<u64, u32>,
 }
 
 impl Xwm {
@@ -219,8 +219,8 @@ impl Xwm {
             client_list: Vec::new(),
             client_list_stacking: Vec::new(),
 
-            xwindows: HashMap::new(),
-            serials: HashMap::new(),
+            xwindows: BTreeMap::new(),
+            serials: BTreeMap::new(),
         })
     }
 
diff --git a/mm-server/src/config.rs b/mm-server/src/config.rs
index e76f8d7..49d1477 100644
--- a/mm-server/src/config.rs
+++ b/mm-server/src/config.rs
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: BUSL-1.1
 
 use std::{
-    collections::HashMap,
+    collections::BTreeMap,
     ffi::{OsStr, OsString},
     net::ToSocketAddrs,
     num::NonZeroU32,
@@ -23,7 +23,7 @@ lazy_static! {
 
 /// Serde representations of the configuration files.
 mod parsed {
-    use std::{collections::HashMap, num::NonZeroU32, path::PathBuf};
+    use std::{collections::BTreeMap, num::NonZeroU32, path::PathBuf};
 
     use converge::Converge;
     use serde::Deserialize;
@@ -65,7 +65,7 @@ mod parsed {
     #[derive(Debug, Clone, PartialEq, Deserialize, Converge)]
     pub(super) struct Config {
         pub(super) include_apps: Option<Vec<PathBuf>>,
-        pub(super) apps: Option<HashMap<String, AppConfig>>,
+        pub(super) apps: Option<BTreeMap<String, AppConfig>>,
 
         pub(super) data_home: Option<PathBuf>,
 
@@ -100,7 +100,7 @@ mod parsed {
     pub(super) struct AppConfig {
         pub(super) description: Option<String>,
         pub(super) command: Vec<String>,
-        pub(super) environment: Option<HashMap<String, String>>,
+        pub(super) environment: Option<BTreeMap<String, String>>,
         pub(super) xwayland: Option<bool>,
         pub(super) force_1x_scale: Option<bool>,
         pub(super) isolate_home: Option<bool>,
@@ -112,7 +112,7 @@ mod parsed {
 #[derive(Debug, Clone, PartialEq)]
 pub struct Config {
     pub server: ServerConfig,
-    pub apps: HashMap<String, AppConfig>,
+    pub apps: BTreeMap<String, AppConfig>,
     pub data_home: PathBuf,
 
     pub bug_report_dir: Option<PathBuf>,
@@ -132,7 +132,7 @@ pub struct ServerConfig {
 pub struct AppConfig {
     pub description: Option<String>,
     pub command: Vec<OsString>,
-    pub env: HashMap<OsString, OsString>,
+    pub env: BTreeMap<OsString, OsString>,
     pub xwayland: bool,
     pub force_1x_scale: bool,
     pub home_isolation_mode: HomeIsolationMode,
@@ -218,8 +218,8 @@ impl Config {
                 },
             },
             data_home: data_home.clone(),
-            apps: HashMap::new(), // Handled below.
-            bug_report_dir: None, // This is only set from the command line.
+            apps: BTreeMap::new(), // Handled below.
+            bug_report_dir: None,  // This is only set from the command line.
         };
 
         // Collect additional app definitions from app_dirs.
@@ -409,7 +409,7 @@ mod test {
         static ref EXAMPLE_APP: AppConfig = AppConfig {
             description: None,
             command: vec!["echo".to_owned().into(), "hello".to_owned().into()],
-            env: HashMap::new(),
+            env: Default::default(),
             xwayland: true,
             force_1x_scale: false,
             home_isolation_mode: HomeIsolationMode::Unisolated,
diff --git a/mm-server/src/server.rs b/mm-server/src/server.rs
index 65509b1..271eaa7 100644
--- a/mm-server/src/server.rs
+++ b/mm-server/src/server.rs
@@ -5,7 +5,7 @@
 mod handlers;
 mod sendmmsg;
 
-use std::collections::{HashMap, VecDeque};
+use std::collections::{BTreeMap, VecDeque};
 use std::net::SocketAddr;
 use std::sync::Arc;
 
@@ -14,6 +14,7 @@ use anyhow::bail;
 use anyhow::Context;
 use bytes::{Buf, Bytes, BytesMut};
 use crossbeam_channel::{Receiver, Sender, TryRecvError};
+use hashbrown::HashMap;
 use mm_protocol as protocol;
 use protocol::error::ErrorCode;
 use ring::rand::{self, SecureRandom};
@@ -69,9 +70,9 @@ pub struct ClientConnection {
     conn: quiche::Connection,
     timer: mio_timerfd::TimerFd,
     timeout_token: mio::Token,
-    partial_reads: HashMap<u64, BytesMut>,
-    partial_writes: HashMap<u64, Bytes>,
-    in_flight: HashMap<u64, StreamWorker>,
+    partial_reads: BTreeMap<u64, BytesMut>,
+    partial_writes: BTreeMap<u64, Bytes>,
+    in_flight: BTreeMap<u64, StreamWorker>,
     dgram_recv: Receiver<protocol::MessageType>,
     dgram_send: WakingSender<protocol::MessageType>,
 }
@@ -448,7 +449,7 @@ impl Server {
                     mio::Interest::READABLE,
                 )?;
 
-                let streams = HashMap::new();
+                let streams = BTreeMap::new();
 
                 let (dgram_send, dgram_recv) = crossbeam_channel::unbounded();
                 let dgram_send = WakingSender::new(self.waker.clone(), dgram_send);
@@ -460,8 +461,8 @@ impl Server {
                     timer,
                     timeout_token,
                     in_flight: streams,
-                    partial_reads: HashMap::new(),
-                    partial_writes: HashMap::new(),
+                    partial_reads: BTreeMap::new(),
+                    partial_writes: BTreeMap::new(),
                     dgram_recv,
                     dgram_send,
                 };
@@ -723,7 +724,7 @@ impl ClientConnection {
 
     /// Flushes previous partial writes.
     fn flush_partial_write(&mut self, sid: u64) -> anyhow::Result<bool> {
-        use std::collections::hash_map::Entry;
+        use std::collections::btree_map::Entry;
 
         match self.partial_writes.entry(sid) {
             Entry::Vacant(_) => Ok(true),
diff --git a/mm-server/src/server/handlers.rs b/mm-server/src/server/handlers.rs
index ad5ca52..72dac67 100644
--- a/mm-server/src/server/handlers.rs
+++ b/mm-server/src/server/handlers.rs
@@ -2,10 +2,9 @@
 //
 // SPDX-License-Identifier: BUSL-1.1
 
-use std::time;
+use std::{collections::BTreeMap, time};
 
 use crossbeam_channel::{select, Receiver};
-use hashbrown::HashMap;
 use mm_protocol as protocol;
 use protocol::error::ErrorCode;
 use tracing::{debug, debug_span, error, trace};
@@ -387,7 +386,7 @@ fn attach(
     let mut pointer_lock = None;
 
     let mut debug_outputs = if bug_report_dir.is_some() {
-        Some(HashMap::<u64, std::fs::File>::new())
+        Some(BTreeMap::<u64, std::fs::File>::new())
     } else {
         None
     };
diff --git a/mm-server/src/state.rs b/mm-server/src/state.rs
index 3102774..aae53ad 100644
--- a/mm-server/src/state.rs
+++ b/mm-server/src/state.rs
@@ -16,6 +16,8 @@ pub type SharedState = Arc<Mutex<ServerState>>;
 const DEFAULT_SESSION_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10 * 60);
 
 pub struct ServerState {
+    // TODO: we'd rather use a BTreeMap, but we want
+    // hash_brown::HashMap::extract_if.
     pub sessions: HashMap<u64, Session>,
     pub cfg: Config,
     pub vk: Arc<VkContext>,