diff --git a/sqlite3vfs/memory.go b/sqlite3vfs/memory.go
index 9721921..697cc1f 100644
--- a/sqlite3vfs/memory.go
+++ b/sqlite3vfs/memory.go
@@ -47,16 +47,23 @@ const memSectorSize = 65536
 //
 // A MemoryDB is safe to access concurrently through multiple SQLite connections.
 type MemoryDB struct {
+	// +checklocks:dataMtx
 	MaxSize int64
 
-	mtx  sync.RWMutex
-	size int64
+	// +checklocks:dataMtx
 	data []*[memSectorSize]byte
+	// +checklocks:dataMtx
+	size int64
 
-	locker   sync.Mutex
-	pending  *memoryFile
+	// +checklocks:lockMtx
+	pending *memoryFile
+	// +checklocks:lockMtx
 	reserved *memoryFile
-	shared   int
+	// +checklocks:lockMtx
+	shared int
+
+	lockMtx sync.Mutex
+	dataMtx sync.RWMutex
 }
 
 // NewMemoryDB creates a new MemoryDB using mem as its initial contents.
@@ -86,6 +93,12 @@ type memoryFile struct {
 	readOnly bool
 }
 
+var (
+	// Ensure these interfaces are implemented:
+	_ FileLockState = &memoryFile{}
+	_ FileSizeHint  = &memoryFile{}
+)
+
 // Close implements the [File] and [io.Closer] interfaces.
 func (m *memoryFile) Close() error {
 	return m.Unlock(LOCK_NONE)
@@ -93,8 +106,8 @@ func (m *memoryFile) Close() error {
 
 // ReadAt implements the [File] and [io.ReaderAt] interfaces.
 func (m *memoryFile) ReadAt(b []byte, off int64) (n int, err error) {
-	m.mtx.RLock()
-	defer m.mtx.RUnlock()
+	m.dataMtx.RLock()
+	defer m.dataMtx.RUnlock()
 
 	if off >= m.size {
 		return 0, io.EOF
@@ -116,10 +129,11 @@ func (m *memoryFile) ReadAt(b []byte, off int64) (n int, err error) {
 
 // WriteAt implements the [File] and [io.WriterAt] interfaces.
 func (m *memoryFile) WriteAt(b []byte, off int64) (n int, err error) {
-	m.mtx.Lock()
-	defer m.mtx.Unlock()
+	m.dataMtx.Lock()
+	defer m.dataMtx.Unlock()
 
-	if m.MaxSize > 0 && off+int64(len(b)) > m.MaxSize {
+	size := off + int64(len(b))
+	if m.MaxSize > 0 && size > m.MaxSize {
 		return 0, _FULL
 	}
 
@@ -133,16 +147,20 @@ func (m *memoryFile) WriteAt(b []byte, off int64) (n int, err error) {
 		// Assume writes are page aligned.
 		return 0, io.ErrShortWrite
 	}
+	if size > m.size {
+		m.size = size
+	}
 	return n, nil
 }
 
 // Truncate implements the [File] interface.
 func (m *memoryFile) Truncate(size int64) error {
-	m.mtx.Lock()
-	defer m.mtx.Unlock()
+	m.dataMtx.Lock()
+	defer m.dataMtx.Unlock()
 	return m.truncate(size)
 }
 
+// +checklocks:m.dataMtx
 func (m *memoryFile) truncate(size int64) error {
 	if m.MaxSize > 0 && size > m.MaxSize {
 		return _FULL
@@ -171,8 +189,8 @@ func (*memoryFile) Sync(flag SyncFlag) error {
 
 // Size implements the [File] interface.
 func (m *memoryFile) Size() (int64, error) {
-	m.mtx.RLock()
-	defer m.mtx.RUnlock()
+	m.dataMtx.RLock()
+	defer m.dataMtx.RUnlock()
 	return m.size, nil
 }
 
@@ -186,8 +204,8 @@ func (m *memoryFile) Lock(lock LockLevel) error {
 		return _IOERR_LOCK
 	}
 
-	m.locker.Lock()
-	defer m.locker.Unlock()
+	m.lockMtx.Lock()
+	defer m.lockMtx.Unlock()
 	deadline := time.Now().Add(time.Millisecond)
 
 	switch lock {
@@ -196,9 +214,9 @@ func (m *memoryFile) Lock(lock LockLevel) error {
 			if time.Now().After(deadline) {
 				return _BUSY
 			}
-			m.locker.Unlock()
+			m.lockMtx.Unlock()
 			runtime.Gosched()
-			m.locker.Lock()
+			m.lockMtx.Lock()
 		}
 		m.shared++
 
@@ -221,9 +239,9 @@ func (m *memoryFile) Lock(lock LockLevel) error {
 			if time.Now().After(deadline) {
 				return _BUSY
 			}
-			m.locker.Unlock()
+			m.lockMtx.Unlock()
 			runtime.Gosched()
-			m.locker.Lock()
+			m.lockMtx.Lock()
 		}
 	}
 
@@ -237,8 +255,8 @@ func (m *memoryFile) Unlock(lock LockLevel) error {
 		return nil
 	}
 
-	m.locker.Lock()
-	defer m.locker.Unlock()
+	m.lockMtx.Lock()
+	defer m.lockMtx.Unlock()
 
 	if m.pending == m {
 		m.pending = nil
@@ -258,8 +276,8 @@ func (m *memoryFile) CheckReservedLock() (bool, error) {
 	if m.lock >= LOCK_RESERVED {
 		return true, nil
 	}
-	m.locker.Lock()
-	defer m.locker.Unlock()
+	m.lockMtx.Lock()
+	defer m.lockMtx.Unlock()
 	return m.reserved != nil, nil
 }
 
@@ -278,8 +296,8 @@ func (*memoryFile) DeviceCharacteristics() DeviceCharacteristic {
 
 // SizeHint implements the [FileSizeHint] interface.
 func (m *memoryFile) SizeHint(size int64) error {
-	m.mtx.Lock()
-	defer m.mtx.Unlock()
+	m.dataMtx.Lock()
+	defer m.dataMtx.Unlock()
 	if size > m.size {
 		return m.truncate(size)
 	}
diff --git a/sqlite3vfs/registry.go b/sqlite3vfs/registry.go
index 3fb946f..ee1b7c6 100644
--- a/sqlite3vfs/registry.go
+++ b/sqlite3vfs/registry.go
@@ -3,6 +3,7 @@ package sqlite3vfs
 import "sync"
 
 var (
+	// +checklocks:vfsRegistryMtx
 	vfsRegistry    map[string]VFS
 	vfsRegistryMtx sync.Mutex
 )
diff --git a/sqlite3vfs/tests/mptest/mptest_test.go b/sqlite3vfs/tests/mptest/mptest_test.go
index 59b8298..e264d12 100644
--- a/sqlite3vfs/tests/mptest/mptest_test.go
+++ b/sqlite3vfs/tests/mptest/mptest_test.go
@@ -214,7 +214,9 @@ func newContext(t *testing.T) context.Context {
 type logger struct{}
 
 type testWriter struct {
+	// +checklocks:mtx
 	*testing.T
+	// +checklocks:mtx
 	buf []byte
 	mtx sync.Mutex
 }