diff --git a/helix-core/src/history.rs b/helix-core/src/history.rs
index 0c56f8f9c4b7b..e2acf373733ad 100644
--- a/helix-core/src/history.rs
+++ b/helix-core/src/history.rs
@@ -190,7 +190,6 @@ const UNDO_FILE_HEADER_LEN: usize = UNDO_FILE_HEADER_TAG.len();
 const UNDO_FILE_VERSION: u8 = 1;
 
 impl History {
-    // TODO: Vim uses magic numbers for each revision. Why?
     pub fn serialize<W: Write + Seek>(
         &self,
         writer: &mut W,
@@ -212,7 +211,6 @@ impl History {
         writer.write_all(&get_hash(&mut std::fs::File::open(path)?)?)?;
 
         // Append new revisions to the end of the file.
-        // TODO: Recompute hash on append
         write_usize(writer, self.revisions.len())?;
         writer.seek(SeekFrom::End(0))?;
         for rev in &self.revisions[last_saved_revision..] {
@@ -279,10 +277,12 @@ impl History {
         if new_revs.is_empty() {
             return Ok(());
         }
+        other.revisions.reserve_exact(n);
 
         // Only unique revisions in `self` matter, so saturating_sub(1) is sound as it going to 0 means there are no new revisions in the other history that aren't in `self`
         let offset = (other.revisions.len() - n).saturating_sub(1);
         for mut r in new_revs {
+            // Update parents of new revisions
             if r.parent >= n {
                 r.parent += offset;
             }
diff --git a/helix-view/src/document.rs b/helix-view/src/document.rs
index f7814cf512fa2..77958cf62fcab 100644
--- a/helix-view/src/document.rs
+++ b/helix-view/src/document.rs
@@ -922,7 +922,6 @@ impl Document {
                 }
             }
 
-            // TODO: Check error handling
             let has_valid_undofile = if undofile_enabled {
                 let path = path.clone();
                 let undofile_path = undofile_path.clone();
@@ -970,20 +969,26 @@ impl Document {
             };
 
             // Set undofile perms
-            // TODO: Vim does (perm & 0707) | ((perm & 07) << 3)
             #[cfg(unix)]
             if undofile_enabled && undofile_res.is_ok() && undofile_path.as_ref().unwrap().exists()
             {
+                use std::os::unix::ffi::OsStrExt;
+                use std::os::unix::fs::{MetadataExt, PermissionsExt};
                 let meta = tokio::fs::metadata(path.as_path()).await?;
 
                 // From https://github.com/uutils/coreutils/blob/2c73e978ba882c9cd56f0f16fae6f8dcce1c9850/src/uucore/src/lib/features/perms.rs#L46-L61
-                use std::os::unix::ffi::OsStrExt;
-                use std::os::unix::fs::MetadataExt;
                 let uid = meta.uid();
                 let gid = meta.gid();
                 let s = std::ffi::CString::new(path.as_os_str().as_bytes())?;
                 let ret = unsafe { libc::chown(s.as_ptr(), uid, gid) };
                 if ret != 0 {
+                    let mut perms = meta.permissions();
+                    let new_perms = (perms.mode() & 0x0707) | (perms.mode() & 0x07) << 3;
+                    perms.set_mode(new_perms);
+
+                    // Ignore errors
+                    let _ = tokio::fs::set_permissions(&undofile_path.unwrap(), perms).await;
+
                     undofile_res = Err(anyhow::anyhow!(tokio::io::Error::last_os_error()));
                 }