diff --git a/bindings/javascript/src/lib.rs b/bindings/javascript/src/lib.rs
index 7d84d6cc3..4b029fdc9 100644
--- a/bindings/javascript/src/lib.rs
+++ b/bindings/javascript/src/lib.rs
@@ -444,8 +444,8 @@ impl DatabaseFile {
 }
 
 impl limbo_core::DatabaseStorage for DatabaseFile {
-    fn read_page(&self, page_idx: usize, c: limbo_core::Completion) -> limbo_core::Result<()> {
-        let r = match c {
+    fn read_page(&self, page_idx: usize, c: Arc<limbo_core::Completion>) -> limbo_core::Result<()> {
+        let r = match *c {
             limbo_core::Completion::Read(ref r) => r,
             _ => unreachable!(),
         };
@@ -463,7 +463,7 @@ impl limbo_core::DatabaseStorage for DatabaseFile {
         &self,
         page_idx: usize,
         buffer: Arc<std::cell::RefCell<limbo_core::Buffer>>,
-        c: limbo_core::Completion,
+        c: Arc<limbo_core::Completion>,
     ) -> limbo_core::Result<()> {
         let size = buffer.borrow().len();
         let pos = (page_idx - 1) * size;
@@ -471,7 +471,7 @@ impl limbo_core::DatabaseStorage for DatabaseFile {
         Ok(())
     }
 
-    fn sync(&self, c: limbo_core::Completion) -> limbo_core::Result<()> {
+    fn sync(&self, c: Arc<limbo_core::Completion>) -> limbo_core::Result<()> {
         self.file.sync(c)
     }
 }
diff --git a/bindings/wasm/lib.rs b/bindings/wasm/lib.rs
index ffbe90928..4277f1f3f 100644
--- a/bindings/wasm/lib.rs
+++ b/bindings/wasm/lib.rs
@@ -208,8 +208,8 @@ impl limbo_core::File for File {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: limbo_core::Completion) -> Result<()> {
-        let r = match &c {
+    fn pread(&self, pos: usize, c: Arc<limbo_core::Completion>) -> Result<()> {
+        let r = match *c {
             limbo_core::Completion::Read(ref r) => r,
             _ => unreachable!(),
         };
@@ -227,9 +227,9 @@ impl limbo_core::File for File {
         &self,
         pos: usize,
         buffer: Arc<std::cell::RefCell<limbo_core::Buffer>>,
-        c: limbo_core::Completion,
+        c: Arc<limbo_core::Completion>,
     ) -> Result<()> {
-        let w = match &c {
+        let w = match *c {
             limbo_core::Completion::Write(ref w) => w,
             _ => unreachable!(),
         };
@@ -240,7 +240,7 @@ impl limbo_core::File for File {
         Ok(())
     }
 
-    fn sync(&self, c: limbo_core::Completion) -> Result<()> {
+    fn sync(&self, c: Arc<limbo_core::Completion>) -> Result<()> {
         self.vfs.sync(self.fd);
         c.complete(0);
         Ok(())
@@ -326,8 +326,8 @@ impl DatabaseFile {
 }
 
 impl limbo_core::DatabaseStorage for DatabaseFile {
-    fn read_page(&self, page_idx: usize, c: limbo_core::Completion) -> Result<()> {
-        let r = match c {
+    fn read_page(&self, page_idx: usize, c: Arc<limbo_core::Completion>) -> Result<()> {
+        let r = match *c {
             limbo_core::Completion::Read(ref r) => r,
             _ => unreachable!(),
         };
@@ -345,7 +345,7 @@ impl limbo_core::DatabaseStorage for DatabaseFile {
         &self,
         page_idx: usize,
         buffer: Arc<std::cell::RefCell<limbo_core::Buffer>>,
-        c: limbo_core::Completion,
+        c: Arc<limbo_core::Completion>,
     ) -> Result<()> {
         let size = buffer.borrow().len();
         let pos = (page_idx - 1) * size;
@@ -353,7 +353,7 @@ impl limbo_core::DatabaseStorage for DatabaseFile {
         Ok(())
     }
 
-    fn sync(&self, _c: limbo_core::Completion) -> Result<()> {
+    fn sync(&self, _c: Arc<limbo_core::Completion>) -> Result<()> {
         todo!()
     }
 }
diff --git a/core/io/generic.rs b/core/io/generic.rs
index aab5f2687..60e11f119 100644
--- a/core/io/generic.rs
+++ b/core/io/generic.rs
@@ -79,11 +79,11 @@ impl File for GenericFile {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: Completion) -> Result<()> {
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()> {
         let mut file = self.file.borrow_mut();
         file.seek(std::io::SeekFrom::Start(pos as u64))?;
         {
-            let r = match c {
+            let r = match *c {
                 Completion::Read(ref r) => r,
                 _ => unreachable!(),
             };
@@ -95,7 +95,7 @@ impl File for GenericFile {
         Ok(())
     }
 
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Completion) -> Result<()> {
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Arc<Completion>) -> Result<()> {
         let mut file = self.file.borrow_mut();
         file.seek(std::io::SeekFrom::Start(pos as u64))?;
         let buf = buffer.borrow();
@@ -105,7 +105,7 @@ impl File for GenericFile {
         Ok(())
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         let mut file = self.file.borrow_mut();
         file.sync_all().map_err(|err| LimboError::IOError(err))?;
         c.complete(0);
diff --git a/core/io/io_uring.rs b/core/io/io_uring.rs
index 25d6aa33e..44d4c5696 100644
--- a/core/io/io_uring.rs
+++ b/core/io/io_uring.rs
@@ -1,3 +1,5 @@
+#![allow(clippy::arc_with_non_send_sync)]
+
 use super::{common, Completion, File, OpenFlags, WriteCompletion, IO};
 use crate::io::clock::{Clock, Instant};
 use crate::{LimboError, MemoryIO, Result};
@@ -93,7 +95,7 @@ impl InnerUringIO {
 }
 
 impl WrappedIOUring {
-    fn submit_entry(&mut self, entry: &io_uring::squeue::Entry, c: Completion) {
+    fn submit_entry(&mut self, entry: &io_uring::squeue::Entry, c: Arc<Completion>) {
         trace!("submit_entry({:?})", entry);
         self.pending[entry.get_user_data() as usize] = Some(c);
         unsafe {
@@ -263,7 +265,7 @@ impl File for UringFile {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: Completion) -> Result<()> {
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()> {
         let r = c.as_read();
         trace!("pread(pos = {}, length = {})", pos, r.buf().len());
         let fd = io_uring::types::Fd(self.file.as_raw_fd());
@@ -282,7 +284,7 @@ impl File for UringFile {
         Ok(())
     }
 
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Completion) -> Result<()> {
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Arc<Completion>) -> Result<()> {
         let mut io = self.io.borrow_mut();
         let fd = io_uring::types::Fd(self.file.as_raw_fd());
         let write = {
diff --git a/core/io/memory.rs b/core/io/memory.rs
index 9cc56a5e3..cb20c6e63 100644
--- a/core/io/memory.rs
+++ b/core/io/memory.rs
@@ -79,7 +79,7 @@ impl File for MemoryFile {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: Completion) -> Result<()> {
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()> {
         let r = c.as_read();
         let buf_len = r.buf().len();
         if buf_len == 0 {
@@ -120,7 +120,7 @@ impl File for MemoryFile {
         Ok(())
     }
 
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Completion) -> Result<()> {
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Arc<Completion>) -> Result<()> {
         let buf = buffer.borrow();
         let buf_len = buf.len();
         if buf_len == 0 {
@@ -156,7 +156,7 @@ impl File for MemoryFile {
         Ok(())
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         // no-op
         c.complete(0);
         Ok(())
diff --git a/core/io/mod.rs b/core/io/mod.rs
index 6f75e9bea..4cbe785c5 100644
--- a/core/io/mod.rs
+++ b/core/io/mod.rs
@@ -14,9 +14,9 @@ use std::{
 pub trait File: Send + Sync {
     fn lock_file(&self, exclusive: bool) -> Result<()>;
     fn unlock_file(&self) -> Result<()>;
-    fn pread(&self, pos: usize, c: Completion) -> Result<()>;
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Completion) -> Result<()>;
-    fn sync(&self, c: Completion) -> Result<()>;
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()>;
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Arc<Completion>) -> Result<()>;
+    fn sync(&self, c: Arc<Completion>) -> Result<()>;
     fn size(&self) -> Result<u64>;
 }
 
diff --git a/core/io/unix.rs b/core/io/unix.rs
index 721ba20f3..8c2f121e3 100644
--- a/core/io/unix.rs
+++ b/core/io/unix.rs
@@ -268,10 +268,10 @@ impl IO for UnixIO {
 }
 
 enum CompletionCallback {
-    Read(Arc<RefCell<std::fs::File>>, Completion, usize),
+    Read(Arc<RefCell<std::fs::File>>, Arc<Completion>, usize),
     Write(
         Arc<RefCell<std::fs::File>>,
-        Completion,
+        Arc<Completion>,
         Arc<RefCell<crate::Buffer>>,
         usize,
     ),
@@ -326,7 +326,7 @@ impl File for UnixFile<'_> {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: Completion) -> Result<()> {
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()> {
         let file = self.file.borrow();
         let result = {
             let r = c.as_read();
@@ -358,7 +358,7 @@ impl File for UnixFile<'_> {
         }
     }
 
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Completion) -> Result<()> {
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<crate::Buffer>>, c: Arc<Completion>) -> Result<()> {
         let file = self.file.borrow();
         let result = {
             let buf = buffer.borrow();
@@ -387,7 +387,7 @@ impl File for UnixFile<'_> {
         }
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         let file = self.file.borrow();
         let result = fs::fsync(file.as_fd());
         match result {
diff --git a/core/io/vfs.rs b/core/io/vfs.rs
index d02f7d345..7e953ebd0 100644
--- a/core/io/vfs.rs
+++ b/core/io/vfs.rs
@@ -93,8 +93,8 @@ impl File for VfsFileImpl {
         Ok(())
     }
 
-    fn pread(&self, pos: usize, c: Completion) -> Result<()> {
-        let r = match &c {
+    fn pread(&self, pos: usize, c: Arc<Completion>) -> Result<()> {
+        let r = match &*c {
             Completion::Read(ref r) => r,
             _ => unreachable!(),
         };
@@ -112,7 +112,7 @@ impl File for VfsFileImpl {
         }
     }
 
-    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Completion) -> Result<()> {
+    fn pwrite(&self, pos: usize, buffer: Arc<RefCell<Buffer>>, c: Arc<Completion>) -> Result<()> {
         let buf = buffer.borrow();
         let count = buf.as_slice().len();
         if self.vfs.is_null() {
@@ -136,7 +136,7 @@ impl File for VfsFileImpl {
         }
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         let vfs = unsafe { &*self.vfs };
         let result = unsafe { (vfs.sync)(self.file) };
         if result < 0 {
diff --git a/core/lib.rs b/core/lib.rs
index 038fc6218..e60d74502 100644
--- a/core/lib.rs
+++ b/core/lib.rs
@@ -1,3 +1,5 @@
+#![allow(clippy::arc_with_non_send_sync)]
+
 mod error;
 mod ext;
 mod fast_lock;
@@ -302,7 +304,8 @@ pub fn maybe_init_database_file(file: &Arc<dyn File>, io: &Arc<dyn IO>) -> Resul
                 let completion = Completion::Write(WriteCompletion::new(Box::new(move |_| {
                     *flag_complete.borrow_mut() = true;
                 })));
-                file.pwrite(0, contents.buffer.clone(), completion)?;
+                #[allow(clippy::arc_with_non_send_sync)]
+                file.pwrite(0, contents.buffer.clone(), Arc::new(completion))?;
             }
             let mut limit = 100;
             loop {
diff --git a/core/storage/btree.rs b/core/storage/btree.rs
index 57e88802a..735f0495e 100644
--- a/core/storage/btree.rs
+++ b/core/storage/btree.rs
@@ -6776,7 +6776,7 @@ mod tests {
 
         let write_complete = Box::new(|_| {});
         let c = Completion::Write(WriteCompletion::new(write_complete));
-        db_file.write_page(1, buf.clone(), c).unwrap();
+        db_file.write_page(1, buf.clone(), Arc::new(c)).unwrap();
 
         let wal_shared = WalFileShared::open_shared(&io, "test.wal", page_size).unwrap();
         let wal = Rc::new(RefCell::new(WalFile::new(
@@ -6826,9 +6826,10 @@ mod tests {
             )));
             let write_complete = Box::new(|_| {});
             let c = Completion::Write(WriteCompletion::new(write_complete));
+            #[allow(clippy::arc_with_non_send_sync)]
             pager
                 .db_file
-                .write_page(current_page as usize, buf.clone(), c)?;
+                .write_page(current_page as usize, buf.clone(), Arc::new(c))?;
             pager.io.run_once()?;
 
             let page = cursor.read_page(current_page as usize)?;
diff --git a/core/storage/database.rs b/core/storage/database.rs
index cf8b57d8e..db57892ae 100644
--- a/core/storage/database.rs
+++ b/core/storage/database.rs
@@ -8,14 +8,14 @@ use std::{cell::RefCell, sync::Arc};
 /// the storage medium. A database can either be a file on disk, like in SQLite,
 /// or something like a remote page server service.
 pub trait DatabaseStorage: Send + Sync {
-    fn read_page(&self, page_idx: usize, c: Completion) -> Result<()>;
+    fn read_page(&self, page_idx: usize, c: Arc<Completion>) -> Result<()>;
     fn write_page(
         &self,
         page_idx: usize,
         buffer: Arc<RefCell<Buffer>>,
-        c: Completion,
+        c: Arc<Completion>,
     ) -> Result<()>;
-    fn sync(&self, c: Completion) -> Result<()>;
+    fn sync(&self, c: Arc<Completion>) -> Result<()>;
 }
 
 #[cfg(feature = "fs")]
@@ -30,7 +30,7 @@ unsafe impl Sync for DatabaseFile {}
 
 #[cfg(feature = "fs")]
 impl DatabaseStorage for DatabaseFile {
-    fn read_page(&self, page_idx: usize, c: Completion) -> Result<()> {
+    fn read_page(&self, page_idx: usize, c: Arc<Completion>) -> Result<()> {
         let r = c.as_read();
         let size = r.buf().len();
         assert!(page_idx > 0);
@@ -46,7 +46,7 @@ impl DatabaseStorage for DatabaseFile {
         &self,
         page_idx: usize,
         buffer: Arc<RefCell<Buffer>>,
-        c: Completion,
+        c: Arc<Completion>,
     ) -> Result<()> {
         let buffer_size = buffer.borrow().len();
         assert!(page_idx > 0);
@@ -58,7 +58,7 @@ impl DatabaseStorage for DatabaseFile {
         Ok(())
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         self.file.sync(c)
     }
 }
@@ -78,8 +78,8 @@ unsafe impl Send for FileMemoryStorage {}
 unsafe impl Sync for FileMemoryStorage {}
 
 impl DatabaseStorage for FileMemoryStorage {
-    fn read_page(&self, page_idx: usize, c: Completion) -> Result<()> {
-        let r = match c {
+    fn read_page(&self, page_idx: usize, c: Arc<Completion>) -> Result<()> {
+        let r = match *c {
             Completion::Read(ref r) => r,
             _ => unreachable!(),
         };
@@ -97,7 +97,7 @@ impl DatabaseStorage for FileMemoryStorage {
         &self,
         page_idx: usize,
         buffer: Arc<RefCell<Buffer>>,
-        c: Completion,
+        c: Arc<Completion>,
     ) -> Result<()> {
         let buffer_size = buffer.borrow().len();
         assert!(buffer_size >= 512);
@@ -108,7 +108,7 @@ impl DatabaseStorage for FileMemoryStorage {
         Ok(())
     }
 
-    fn sync(&self, c: Completion) -> Result<()> {
+    fn sync(&self, c: Arc<Completion>) -> Result<()> {
         self.file.sync(c)
     }
 }
diff --git a/core/storage/sqlite3_ondisk.rs b/core/storage/sqlite3_ondisk.rs
index 30035d1ab..dcbed64d0 100644
--- a/core/storage/sqlite3_ondisk.rs
+++ b/core/storage/sqlite3_ondisk.rs
@@ -41,6 +41,8 @@
 //!
 //! https://www.sqlite.org/fileformat.html
 
+#![allow(clippy::arc_with_non_send_sync)]
+
 use crate::error::LimboError;
 use crate::fast_lock::SpinLock;
 use crate::io::{Buffer, Complete, Completion, ReadCompletion, SyncCompletion, WriteCompletion};
@@ -293,7 +295,8 @@ pub fn begin_read_database_header(
         finish_read_database_header(buf, header).unwrap();
     });
     let c = Completion::Read(ReadCompletion::new(buf, complete));
-    db_file.read_page(1, c)?;
+    #[allow(clippy::arc_with_non_send_sync)]
+    db_file.read_page(1, Arc::new(c))?;
     Ok(result)
 }
 
@@ -355,7 +358,8 @@ pub fn begin_write_database_header(header: &DatabaseHeader, pager: &Pager) -> Re
     #[allow(clippy::arc_with_non_send_sync)]
     let buf = Arc::new(RefCell::new(Buffer::allocate(512, drop_fn)));
     let c = Completion::Read(ReadCompletion::new(buf, read_complete));
-    page_source.read_page(1, c)?;
+    #[allow(clippy::arc_with_non_send_sync)]
+    page_source.read_page(1, Arc::new(c))?;
     // run get header block
     pager.io.run_once()?;
 
@@ -369,7 +373,7 @@ pub fn begin_write_database_header(header: &DatabaseHeader, pager: &Pager) -> Re
     });
 
     let c = Completion::Write(WriteCompletion::new(write_complete));
-    page_source.write_page(1, buffer_to_copy, c)?;
+    page_source.write_page(1, buffer_to_copy, Arc::new(c))?;
 
     Ok(())
 }
@@ -819,7 +823,7 @@ pub fn begin_read_page(
         }
     });
     let c = Completion::Read(ReadCompletion::new(buf, complete));
-    db_file.read_page(page_idx, c)?;
+    db_file.read_page(page_idx, Arc::new(c))?;
     Ok(())
 }
 
@@ -877,7 +881,7 @@ pub fn begin_write_btree_page(
         })
     };
     let c = Completion::Write(WriteCompletion::new(write_complete));
-    page_source.write_page(page_id, buffer.clone(), c)?;
+    page_source.write_page(page_id, buffer.clone(), Arc::new(c))?;
     Ok(())
 }
 
@@ -889,7 +893,8 @@ pub fn begin_sync(db_file: Arc<dyn DatabaseStorage>, syncing: Rc<RefCell<bool>>)
             *syncing.borrow_mut() = false;
         }),
     });
-    db_file.sync(completion)?;
+    #[allow(clippy::arc_with_non_send_sync)]
+    db_file.sync(Arc::new(completion))?;
     Ok(())
 }
 
@@ -1519,7 +1524,7 @@ pub fn read_entire_wal_dumb(file: &Arc<dyn File>) -> Result<Arc<UnsafeCell<WalFi
         wfs_data.loaded.store(true, Ordering::SeqCst);
     });
     let c = Completion::Read(ReadCompletion::new(buf_for_pread, complete));
-    file.pread(0, c)?;
+    file.pread(0, Arc::new(c))?;
 
     Ok(wal_file_shared_ret)
 }
@@ -1536,9 +1541,9 @@ pub fn begin_read_wal_frame(
         let buffer_pool = buffer_pool.clone();
         buffer_pool.put(buf);
     });
-    #[allow(clippy::arc_with_non_send_sync)]
     let buf = Arc::new(RefCell::new(Buffer::new(buf, drop_fn)));
-    let c = Completion::Read(ReadCompletion::new(buf, complete));
+    #[allow(clippy::arc_with_non_send_sync)]
+    let c = Arc::new(Completion::Read(ReadCompletion::new(buf, complete)));
     io.pread(offset, c)?;
     Ok(())
 }
@@ -1622,7 +1627,8 @@ pub fn begin_write_wal_frame(
             }
         })
     };
-    let c = Completion::Write(WriteCompletion::new(write_complete));
+    #[allow(clippy::arc_with_non_send_sync)]
+    let c = Arc::new(Completion::Write(WriteCompletion::new(write_complete)));
     io.pwrite(offset, buffer.clone(), c)?;
     trace!("Frame written and synced at offset={offset}");
     Ok(checksums)
@@ -1657,7 +1663,8 @@ pub fn begin_write_wal_header(io: &Arc<dyn File>, header: &WalHeader) -> Result<
             }
         })
     };
-    let c = Completion::Write(WriteCompletion::new(write_complete));
+    #[allow(clippy::arc_with_non_send_sync)]
+    let c = Arc::new(Completion::Write(WriteCompletion::new(write_complete)));
     io.pwrite(0, buffer.clone(), c)?;
     Ok(())
 }
diff --git a/core/storage/wal.rs b/core/storage/wal.rs
index edb657f39..4eab23e44 100644
--- a/core/storage/wal.rs
+++ b/core/storage/wal.rs
@@ -1,3 +1,5 @@
+#![allow(clippy::arc_with_non_send_sync)]
+
 use std::cell::UnsafeCell;
 use std::collections::HashMap;
 use tracing::{debug, trace};
@@ -750,7 +752,7 @@ impl Wal for WalFile {
                             *syncing.borrow_mut() = false;
                         }),
                     });
-                    shared.file.sync(completion)?;
+                    shared.file.sync(Arc::new(completion))?;
                 }
                 self.sync_state.replace(SyncState::Syncing);
                 Ok(WalFsyncStatus::IO)
diff --git a/simulator/runner/file.rs b/simulator/runner/file.rs
index 3e66a02fa..5d1c2cd4b 100644
--- a/simulator/runner/file.rs
+++ b/simulator/runner/file.rs
@@ -77,7 +77,7 @@ impl File for SimulatorFile {
         self.inner.unlock_file()
     }
 
-    fn pread(&self, pos: usize, c: limbo_core::Completion) -> Result<()> {
+    fn pread(&self, pos: usize, c: Arc<limbo_core::Completion>) -> Result<()> {
         *self.nr_pread_calls.borrow_mut() += 1;
         if *self.fault.borrow() {
             *self.nr_pread_faults.borrow_mut() += 1;
@@ -92,7 +92,7 @@ impl File for SimulatorFile {
         &self,
         pos: usize,
         buffer: Arc<RefCell<limbo_core::Buffer>>,
-        c: limbo_core::Completion,
+        c: Arc<limbo_core::Completion>,
     ) -> Result<()> {
         *self.nr_pwrite_calls.borrow_mut() += 1;
         if *self.fault.borrow() {
@@ -104,7 +104,7 @@ impl File for SimulatorFile {
         self.inner.pwrite(pos, buffer, c)
     }
 
-    fn sync(&self, c: limbo_core::Completion) -> Result<()> {
+    fn sync(&self, c: Arc<limbo_core::Completion>) -> Result<()> {
         *self.nr_sync_calls.borrow_mut() += 1;
         self.inner.sync(c)
     }