diff --git a/flake.nix b/flake.nix
index f91122f..6c0ecae 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,16 +30,15 @@
         rustToolchain = fenix.packages.${system}.fromToolchainFile {
           file = ./rust-toolchain.toml;
           # When the file changes, this hash must be updated.
-          sha256 = "sha256-Hn2uaQzRLidAWpfmRwSRdImifGUCAb9HeAqTYFXWeQk=";
+          sha256 = "sha256-Qxt8XAuaUR2OMdKbN4u8dBJOhSHxS+uS06Wl9+flVEk=";
         };
 
         # Nightly toolchain for rustfmt (pinned to current flake lock)
         # Note that the github CI uses "current nightly" for formatting, it 's not pinned.
-        rustNightly = fenix.packages.${system}.latest.toolchain;
-        rustNightlyFmt = fenix.packages.${system}.latest.rustfmt;
+        rustNightly = fenix.packages.${system}.latest;
 
         craneLib = (crane.mkLib pkgs).overrideToolchain rustToolchain;
-        craneLibNightly = (crane.mkLib pkgs).overrideToolchain rustNightly;
+        craneLibNightly = (crane.mkLib pkgs).overrideToolchain rustNightly.toolchain;
 
         src = lib.fileset.toSource {
           root = ./.;
@@ -97,11 +96,15 @@
           checks = self.checks.${system};
 
           packages = with pkgs; [
-            rustNightlyFmt
             cargo-tarpaulin
             cargo-watch
             sqlite
           ];
+
+          shellHook = ''
+            # Prepend nightly rustfmt to PATH.
+            export PATH="${rustNightly.rustfmt}/bin:$PATH"
+          '';
         };
       }
     );
diff --git a/src/base.rs b/src/base.rs
index 9d5b7a4..d191b80 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -2049,7 +2049,7 @@ fn complete_msgbar(text: &EditRope, cursor: &mut Cursor, store: &ChatStore) -> V
         // Complete Emoji shortcodes.
         Some(':') => {
             let list = store.emojis.complete(&id[1..]);
-            let iter = list.into_iter().take(200).map(|s| format!(":{}:", s));
+            let iter = list.into_iter().take(200).map(|s| format!(":{s}:"));
 
             return iter.collect();
         },
@@ -2195,7 +2195,7 @@ pub mod tests {
         ));
 
         for i in 0..3 {
-            let event_id = format!("$house_{}", i);
+            let event_id = format!("$house_{i}");
             info.insert_reaction(MessageLikeEvent::Original(
                 matrix_sdk::ruma::events::OriginalMessageLikeEvent {
                     content: content.clone(),
@@ -2214,7 +2214,7 @@ pub mod tests {
         ));
 
         for i in 0..2 {
-            let event_id = format!("$smile_{}", i);
+            let event_id = format!("$smile_{i}");
             info.insert_reaction(MessageLikeEvent::Original(
                 matrix_sdk::ruma::events::OriginalMessageLikeEvent {
                     content: content.clone(),
@@ -2228,7 +2228,7 @@ pub mod tests {
         }
 
         for i in 2..4 {
-            let event_id = format!("$smile_{}", i);
+            let event_id = format!("$smile_{i}");
             info.insert_reaction(MessageLikeEvent::Original(
                 matrix_sdk::ruma::events::OriginalMessageLikeEvent {
                     content: content.clone(),
diff --git a/src/config.rs b/src/config.rs
index b3d931d..e7a4a47 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -932,10 +932,7 @@ impl ApplicationSettings {
         } else {
             loop {
                 println!("\nNo profile specified. Available profiles:");
-                profiles
-                    .keys()
-                    .enumerate()
-                    .for_each(|(i, name)| println!("{}: {}", i, name));
+                profiles.keys().enumerate().for_each(|(i, name)| println!("{i}: {name}"));
 
                 print!("Select a number or 'q' to quit: ");
                 let _ = std::io::stdout().flush();
diff --git a/src/message/state.rs b/src/message/state.rs
index 53885c4..6756140 100644
--- a/src/message/state.rs
+++ b/src/message/state.rs
@@ -121,11 +121,11 @@ pub fn body_cow_state(ev: &AnySyncStateEvent) -> Cow<'static, str> {
 
             match (old_canon, new_canon) {
                 (None, Some(canon)) => {
-                    format!("* updated the canonical alias for the room to: {}", canon)
+                    format!("* updated the canonical alias for the room to: {canon}")
                 },
                 (Some(old), Some(new)) => {
                     if old != new {
-                        format!("* updated the canonical alias for the room to: {}", new)
+                        format!("* updated the canonical alias for the room to: {new}")
                     } else {
                         return Cow::Borrowed("* removed the canonical alias for the room");
                     }
@@ -187,10 +187,10 @@ pub fn body_cow_state(ev: &AnySyncStateEvent) -> Cow<'static, str> {
 
             match change {
                 MembershipChange::None => {
-                    format!("* did nothing to {}", state_key)
+                    format!("* did nothing to {state_key}")
                 },
                 MembershipChange::Error => {
-                    format!("* failed to calculate membership change to {}", state_key)
+                    format!("* failed to calculate membership change to {state_key}")
                 },
                 MembershipChange::Joined => {
                     return Cow::Borrowed("* joined the room");
@@ -199,19 +199,19 @@ pub fn body_cow_state(ev: &AnySyncStateEvent) -> Cow<'static, str> {
                     return Cow::Borrowed("* left the room");
                 },
                 MembershipChange::Banned => {
-                    format!("* banned {} from the room", state_key)
+                    format!("* banned {state_key} from the room")
                 },
                 MembershipChange::Unbanned => {
-                    format!("* unbanned {} from the room", state_key)
+                    format!("* unbanned {state_key} from the room")
                 },
                 MembershipChange::Kicked => {
-                    format!("* kicked {} from the room", state_key)
+                    format!("* kicked {state_key} from the room")
                 },
                 MembershipChange::Invited => {
-                    format!("* invited {} to the room", state_key)
+                    format!("* invited {state_key} to the room")
                 },
                 MembershipChange::KickedAndBanned => {
-                    format!("* kicked and banned {} from the room", state_key)
+                    format!("* kicked and banned {state_key} from the room")
                 },
                 MembershipChange::InvitationAccepted => {
                     return Cow::Borrowed("* accepted an invitation to join the room");
@@ -220,26 +220,26 @@ pub fn body_cow_state(ev: &AnySyncStateEvent) -> Cow<'static, str> {
                     return Cow::Borrowed("* rejected an invitation to join the room");
                 },
                 MembershipChange::InvitationRevoked => {
-                    format!("* revoked an invitation for {} to join the room", state_key)
+                    format!("* revoked an invitation for {state_key} to join the room")
                 },
                 MembershipChange::Knocked => {
                     return Cow::Borrowed("* would like to join the room");
                 },
                 MembershipChange::KnockAccepted => {
-                    format!("* accepted the room knock from {}", state_key)
+                    format!("* accepted the room knock from {state_key}")
                 },
                 MembershipChange::KnockRetracted => {
                     return Cow::Borrowed("* retracted their room knock");
                 },
                 MembershipChange::KnockDenied => {
-                    format!("* rejected the room knock from {}", state_key)
+                    format!("* rejected the room knock from {state_key}")
                 },
                 MembershipChange::ProfileChanged { displayname_change, avatar_url_change } => {
                     match (displayname_change, avatar_url_change) {
                         (Some(change), avatar_change) => {
                             let mut m = match (change.old, change.new) {
                                 (None, Some(new)) => {
-                                    format!("* set their display name to {:?}", new)
+                                    format!("* set their display name to {new:?}")
                                 },
                                 (Some(old), Some(new)) => {
                                     format!("* changed their display name from {old} to {new}")
@@ -280,7 +280,7 @@ pub fn body_cow_state(ev: &AnySyncStateEvent) -> Cow<'static, str> {
                     }
                 },
                 ev => {
-                    format!("* made an unknown membership change to {}: {:?}", state_key, ev)
+                    format!("* made an unknown membership change to {state_key}: {ev:?}")
                 },
             }
         },
@@ -727,7 +727,7 @@ pub fn html_state(ev: &AnySyncStateEvent) -> StyleTree {
                 ev => {
                     let prefix =
                         StyleTreeNode::Text("* made an unknown membership change to ".into());
-                    let suffix = StyleTreeNode::Text(format!(": {:?}", ev).into());
+                    let suffix = StyleTreeNode::Text(format!(": {ev:?}").into());
                     vec![prefix, user_id, suffix]
                 },
             }
diff --git a/src/windows/room/chat.rs b/src/windows/room/chat.rs
index fbba33c..3a518aa 100644
--- a/src/windows/room/chat.rs
+++ b/src/windows/room/chat.rs
@@ -273,9 +273,9 @@ impl ChatState {
                             let mut filename_incr = filename.clone();
                             for n in 1..=1000 {
                                 if let Some(ext) = ext.and_then(OsStr::to_str) {
-                                    filename_incr.set_file_name(format!("{}-{}.{}", stem, n, ext));
+                                    filename_incr.set_file_name(format!("{stem}-{n}.{ext}"));
                                 } else {
-                                    filename_incr.set_file_name(format!("{}-{}", stem, n));
+                                    filename_incr.set_file_name(format!("{stem}-{n}"));
                                 }
 
                                 if !filename_incr.exists() {
@@ -401,7 +401,7 @@ impl ChatState {
                 };
 
                 if info.user_reactions_contains(&settings.profile.user_id, &event_id, &emoji) {
-                    let msg = format!("You’ve already reacted to this message with {}", emoji);
+                    let msg = format!("You’ve already reacted to this message with {emoji}");
                     let err = UIError::Failure(msg);
 
                     return Err(err);
diff --git a/src/windows/room/mod.rs b/src/windows/room/mod.rs
index 0946f8e..6230052 100644
--- a/src/windows/room/mod.rs
+++ b/src/windows/room/mod.rs
@@ -120,19 +120,19 @@ fn hist_visibility_mode(name: impl Into<String>) -> IambResult<HistoryVisibility
 /// that operations like sending and accepting invites, opening the members window, etc., all work
 /// similarly.
 pub enum RoomState {
-    Chat(ChatState),
-    Space(SpaceState),
+    Chat(Box<ChatState>),
+    Space(Box<SpaceState>),
 }
 
 impl From<ChatState> for RoomState {
     fn from(chat: ChatState) -> Self {
-        RoomState::Chat(chat)
+        RoomState::Chat(Box::new(chat))
     }
 }
 
 impl From<SpaceState> for RoomState {
     fn from(space: SpaceState) -> Self {
-        RoomState::Space(space)
+        RoomState::Space(Box::new(space))
     }
 }
 
@@ -776,8 +776,8 @@ impl WindowOps<IambInfo> for RoomState {
 
     fn dup(&self, store: &mut ProgramStore) -> Self {
         match self {
-            RoomState::Chat(chat) => RoomState::Chat(chat.dup(store)),
-            RoomState::Space(space) => RoomState::Space(space.dup(store)),
+            RoomState::Chat(chat) => RoomState::Chat(Box::new(chat.dup(store))),
+            RoomState::Space(space) => RoomState::Space(Box::new(space.dup(store))),
         }
     }