diff --git a/README.md b/README.md
index 8c4908f..e947214 100644
--- a/README.md
+++ b/README.md
@@ -15,5 +15,5 @@ Roadmap:
 - [x] port [`test_demovfs.c`](https://www.sqlite.org/src/doc/trunk/src/test_demovfs.c) to Go
   - branch [`wasi`](https://github.com/ncruces/go-sqlite3/tree/wasi) uses `test_demovfs.c` directly
 - [x] come up with a simple, nice API, enough for simple queries
-- [ ] file locking, compatible with SQLite on Windows/Unix
-- [ ] ~shared-memory, compatible with SQLite on Windows/Unix~
\ No newline at end of file
+- [x] file locking, compatible with SQLite on Unix
+- [ ] file locking, compatible with SQLite on Windows
\ No newline at end of file
diff --git a/const.go b/const.go
index 0904b87..a5f2ddf 100644
--- a/const.go
+++ b/const.go
@@ -47,82 +47,85 @@ const (
 	WARNING    ErrorCode = 28 /* Warnings from sqlite3_log() */
 )
 
-type ExtendedErrorCode uint16
+type (
+	ExtendedErrorCode uint16
+	xErrorCode        = ExtendedErrorCode
+)
 
 const (
-	ERROR_MISSING_COLLSEQ   = ExtendedErrorCode(ERROR) | (1 << 8)
-	ERROR_RETRY             = ExtendedErrorCode(ERROR) | (2 << 8)
-	ERROR_SNAPSHOT          = ExtendedErrorCode(ERROR) | (3 << 8)
-	IOERR_READ              = ExtendedErrorCode(IOERR) | (1 << 8)
-	IOERR_SHORT_READ        = ExtendedErrorCode(IOERR) | (2 << 8)
-	IOERR_WRITE             = ExtendedErrorCode(IOERR) | (3 << 8)
-	IOERR_FSYNC             = ExtendedErrorCode(IOERR) | (4 << 8)
-	IOERR_DIR_FSYNC         = ExtendedErrorCode(IOERR) | (5 << 8)
-	IOERR_TRUNCATE          = ExtendedErrorCode(IOERR) | (6 << 8)
-	IOERR_FSTAT             = ExtendedErrorCode(IOERR) | (7 << 8)
-	IOERR_UNLOCK            = ExtendedErrorCode(IOERR) | (8 << 8)
-	IOERR_RDLOCK            = ExtendedErrorCode(IOERR) | (9 << 8)
-	IOERR_DELETE            = ExtendedErrorCode(IOERR) | (10 << 8)
-	IOERR_BLOCKED           = ExtendedErrorCode(IOERR) | (11 << 8)
-	IOERR_NOMEM             = ExtendedErrorCode(IOERR) | (12 << 8)
-	IOERR_ACCESS            = ExtendedErrorCode(IOERR) | (13 << 8)
-	IOERR_CHECKRESERVEDLOCK = ExtendedErrorCode(IOERR) | (14 << 8)
-	IOERR_LOCK              = ExtendedErrorCode(IOERR) | (15 << 8)
-	IOERR_CLOSE             = ExtendedErrorCode(IOERR) | (16 << 8)
-	IOERR_DIR_CLOSE         = ExtendedErrorCode(IOERR) | (17 << 8)
-	IOERR_SHMOPEN           = ExtendedErrorCode(IOERR) | (18 << 8)
-	IOERR_SHMSIZE           = ExtendedErrorCode(IOERR) | (19 << 8)
-	IOERR_SHMLOCK           = ExtendedErrorCode(IOERR) | (20 << 8)
-	IOERR_SHMMAP            = ExtendedErrorCode(IOERR) | (21 << 8)
-	IOERR_SEEK              = ExtendedErrorCode(IOERR) | (22 << 8)
-	IOERR_DELETE_NOENT      = ExtendedErrorCode(IOERR) | (23 << 8)
-	IOERR_MMAP              = ExtendedErrorCode(IOERR) | (24 << 8)
-	IOERR_GETTEMPPATH       = ExtendedErrorCode(IOERR) | (25 << 8)
-	IOERR_CONVPATH          = ExtendedErrorCode(IOERR) | (26 << 8)
-	IOERR_VNODE             = ExtendedErrorCode(IOERR) | (27 << 8)
-	IOERR_AUTH              = ExtendedErrorCode(IOERR) | (28 << 8)
-	IOERR_BEGIN_ATOMIC      = ExtendedErrorCode(IOERR) | (29 << 8)
-	IOERR_COMMIT_ATOMIC     = ExtendedErrorCode(IOERR) | (30 << 8)
-	IOERR_ROLLBACK_ATOMIC   = ExtendedErrorCode(IOERR) | (31 << 8)
-	IOERR_DATA              = ExtendedErrorCode(IOERR) | (32 << 8)
-	IOERR_CORRUPTFS         = ExtendedErrorCode(IOERR) | (33 << 8)
-	LOCKED_SHAREDCACHE      = ExtendedErrorCode(LOCKED) | (1 << 8)
-	LOCKED_VTAB             = ExtendedErrorCode(LOCKED) | (2 << 8)
-	BUSY_RECOVERY           = ExtendedErrorCode(BUSY) | (1 << 8)
-	BUSY_SNAPSHOT           = ExtendedErrorCode(BUSY) | (2 << 8)
-	BUSY_TIMEOUT            = ExtendedErrorCode(BUSY) | (3 << 8)
-	CANTOPEN_NOTEMPDIR      = ExtendedErrorCode(CANTOPEN) | (1 << 8)
-	CANTOPEN_ISDIR          = ExtendedErrorCode(CANTOPEN) | (2 << 8)
-	CANTOPEN_FULLPATH       = ExtendedErrorCode(CANTOPEN) | (3 << 8)
-	CANTOPEN_CONVPATH       = ExtendedErrorCode(CANTOPEN) | (4 << 8)
-	CANTOPEN_DIRTYWAL       = ExtendedErrorCode(CANTOPEN) | (5 << 8) /* Not Used */
-	CANTOPEN_SYMLINK        = ExtendedErrorCode(CANTOPEN) | (6 << 8)
-	CORRUPT_VTAB            = ExtendedErrorCode(CORRUPT) | (1 << 8)
-	CORRUPT_SEQUENCE        = ExtendedErrorCode(CORRUPT) | (2 << 8)
-	CORRUPT_INDEX           = ExtendedErrorCode(CORRUPT) | (3 << 8)
-	READONLY_RECOVERY       = ExtendedErrorCode(READONLY) | (1 << 8)
-	READONLY_CANTLOCK       = ExtendedErrorCode(READONLY) | (2 << 8)
-	READONLY_ROLLBACK       = ExtendedErrorCode(READONLY) | (3 << 8)
-	READONLY_DBMOVED        = ExtendedErrorCode(READONLY) | (4 << 8)
-	READONLY_CANTINIT       = ExtendedErrorCode(READONLY) | (5 << 8)
-	READONLY_DIRECTORY      = ExtendedErrorCode(READONLY) | (6 << 8)
-	ABORT_ROLLBACK          = ExtendedErrorCode(ABORT) | (2 << 8)
-	CONSTRAINT_CHECK        = ExtendedErrorCode(CONSTRAINT) | (1 << 8)
-	CONSTRAINT_COMMITHOOK   = ExtendedErrorCode(CONSTRAINT) | (2 << 8)
-	CONSTRAINT_FOREIGNKEY   = ExtendedErrorCode(CONSTRAINT) | (3 << 8)
-	CONSTRAINT_FUNCTION     = ExtendedErrorCode(CONSTRAINT) | (4 << 8)
-	CONSTRAINT_NOTNULL      = ExtendedErrorCode(CONSTRAINT) | (5 << 8)
-	CONSTRAINT_PRIMARYKEY   = ExtendedErrorCode(CONSTRAINT) | (6 << 8)
-	CONSTRAINT_TRIGGER      = ExtendedErrorCode(CONSTRAINT) | (7 << 8)
-	CONSTRAINT_UNIQUE       = ExtendedErrorCode(CONSTRAINT) | (8 << 8)
-	CONSTRAINT_VTAB         = ExtendedErrorCode(CONSTRAINT) | (9 << 8)
-	CONSTRAINT_ROWID        = ExtendedErrorCode(CONSTRAINT) | (10 << 8)
-	CONSTRAINT_PINNED       = ExtendedErrorCode(CONSTRAINT) | (11 << 8)
-	CONSTRAINT_DATATYPE     = ExtendedErrorCode(CONSTRAINT) | (12 << 8)
-	NOTICE_RECOVER_WAL      = ExtendedErrorCode(NOTICE) | (1 << 8)
-	NOTICE_RECOVER_ROLLBACK = ExtendedErrorCode(NOTICE) | (2 << 8)
-	WARNING_AUTOINDEX       = ExtendedErrorCode(WARNING) | (1 << 8)
-	AUTH_USER               = ExtendedErrorCode(AUTH) | (1 << 8)
+	ERROR_MISSING_COLLSEQ   ExtendedErrorCode = xErrorCode(ERROR) | (1 << 8)
+	ERROR_RETRY             ExtendedErrorCode = xErrorCode(ERROR) | (2 << 8)
+	ERROR_SNAPSHOT          ExtendedErrorCode = xErrorCode(ERROR) | (3 << 8)
+	IOERR_READ              ExtendedErrorCode = xErrorCode(IOERR) | (1 << 8)
+	IOERR_SHORT_READ        ExtendedErrorCode = xErrorCode(IOERR) | (2 << 8)
+	IOERR_WRITE             ExtendedErrorCode = xErrorCode(IOERR) | (3 << 8)
+	IOERR_FSYNC             ExtendedErrorCode = xErrorCode(IOERR) | (4 << 8)
+	IOERR_DIR_FSYNC         ExtendedErrorCode = xErrorCode(IOERR) | (5 << 8)
+	IOERR_TRUNCATE          ExtendedErrorCode = xErrorCode(IOERR) | (6 << 8)
+	IOERR_FSTAT             ExtendedErrorCode = xErrorCode(IOERR) | (7 << 8)
+	IOERR_UNLOCK            ExtendedErrorCode = xErrorCode(IOERR) | (8 << 8)
+	IOERR_RDLOCK            ExtendedErrorCode = xErrorCode(IOERR) | (9 << 8)
+	IOERR_DELETE            ExtendedErrorCode = xErrorCode(IOERR) | (10 << 8)
+	IOERR_BLOCKED           ExtendedErrorCode = xErrorCode(IOERR) | (11 << 8)
+	IOERR_NOMEM             ExtendedErrorCode = xErrorCode(IOERR) | (12 << 8)
+	IOERR_ACCESS            ExtendedErrorCode = xErrorCode(IOERR) | (13 << 8)
+	IOERR_CHECKRESERVEDLOCK ExtendedErrorCode = xErrorCode(IOERR) | (14 << 8)
+	IOERR_LOCK              ExtendedErrorCode = xErrorCode(IOERR) | (15 << 8)
+	IOERR_CLOSE             ExtendedErrorCode = xErrorCode(IOERR) | (16 << 8)
+	IOERR_DIR_CLOSE         ExtendedErrorCode = xErrorCode(IOERR) | (17 << 8)
+	IOERR_SHMOPEN           ExtendedErrorCode = xErrorCode(IOERR) | (18 << 8)
+	IOERR_SHMSIZE           ExtendedErrorCode = xErrorCode(IOERR) | (19 << 8)
+	IOERR_SHMLOCK           ExtendedErrorCode = xErrorCode(IOERR) | (20 << 8)
+	IOERR_SHMMAP            ExtendedErrorCode = xErrorCode(IOERR) | (21 << 8)
+	IOERR_SEEK              ExtendedErrorCode = xErrorCode(IOERR) | (22 << 8)
+	IOERR_DELETE_NOENT      ExtendedErrorCode = xErrorCode(IOERR) | (23 << 8)
+	IOERR_MMAP              ExtendedErrorCode = xErrorCode(IOERR) | (24 << 8)
+	IOERR_GETTEMPPATH       ExtendedErrorCode = xErrorCode(IOERR) | (25 << 8)
+	IOERR_CONVPATH          ExtendedErrorCode = xErrorCode(IOERR) | (26 << 8)
+	IOERR_VNODE             ExtendedErrorCode = xErrorCode(IOERR) | (27 << 8)
+	IOERR_AUTH              ExtendedErrorCode = xErrorCode(IOERR) | (28 << 8)
+	IOERR_BEGIN_ATOMIC      ExtendedErrorCode = xErrorCode(IOERR) | (29 << 8)
+	IOERR_COMMIT_ATOMIC     ExtendedErrorCode = xErrorCode(IOERR) | (30 << 8)
+	IOERR_ROLLBACK_ATOMIC   ExtendedErrorCode = xErrorCode(IOERR) | (31 << 8)
+	IOERR_DATA              ExtendedErrorCode = xErrorCode(IOERR) | (32 << 8)
+	IOERR_CORRUPTFS         ExtendedErrorCode = xErrorCode(IOERR) | (33 << 8)
+	LOCKED_SHAREDCACHE      ExtendedErrorCode = xErrorCode(LOCKED) | (1 << 8)
+	LOCKED_VTAB             ExtendedErrorCode = xErrorCode(LOCKED) | (2 << 8)
+	BUSY_RECOVERY           ExtendedErrorCode = xErrorCode(BUSY) | (1 << 8)
+	BUSY_SNAPSHOT           ExtendedErrorCode = xErrorCode(BUSY) | (2 << 8)
+	BUSY_TIMEOUT            ExtendedErrorCode = xErrorCode(BUSY) | (3 << 8)
+	CANTOPEN_NOTEMPDIR      ExtendedErrorCode = xErrorCode(CANTOPEN) | (1 << 8)
+	CANTOPEN_ISDIR          ExtendedErrorCode = xErrorCode(CANTOPEN) | (2 << 8)
+	CANTOPEN_FULLPATH       ExtendedErrorCode = xErrorCode(CANTOPEN) | (3 << 8)
+	CANTOPEN_CONVPATH       ExtendedErrorCode = xErrorCode(CANTOPEN) | (4 << 8)
+	CANTOPEN_DIRTYWAL       ExtendedErrorCode = xErrorCode(CANTOPEN) | (5 << 8) /* Not Used */
+	CANTOPEN_SYMLINK        ExtendedErrorCode = xErrorCode(CANTOPEN) | (6 << 8)
+	CORRUPT_VTAB            ExtendedErrorCode = xErrorCode(CORRUPT) | (1 << 8)
+	CORRUPT_SEQUENCE        ExtendedErrorCode = xErrorCode(CORRUPT) | (2 << 8)
+	CORRUPT_INDEX           ExtendedErrorCode = xErrorCode(CORRUPT) | (3 << 8)
+	READONLY_RECOVERY       ExtendedErrorCode = xErrorCode(READONLY) | (1 << 8)
+	READONLY_CANTLOCK       ExtendedErrorCode = xErrorCode(READONLY) | (2 << 8)
+	READONLY_ROLLBACK       ExtendedErrorCode = xErrorCode(READONLY) | (3 << 8)
+	READONLY_DBMOVED        ExtendedErrorCode = xErrorCode(READONLY) | (4 << 8)
+	READONLY_CANTINIT       ExtendedErrorCode = xErrorCode(READONLY) | (5 << 8)
+	READONLY_DIRECTORY      ExtendedErrorCode = xErrorCode(READONLY) | (6 << 8)
+	ABORT_ROLLBACK          ExtendedErrorCode = xErrorCode(ABORT) | (2 << 8)
+	CONSTRAINT_CHECK        ExtendedErrorCode = xErrorCode(CONSTRAINT) | (1 << 8)
+	CONSTRAINT_COMMITHOOK   ExtendedErrorCode = xErrorCode(CONSTRAINT) | (2 << 8)
+	CONSTRAINT_FOREIGNKEY   ExtendedErrorCode = xErrorCode(CONSTRAINT) | (3 << 8)
+	CONSTRAINT_FUNCTION     ExtendedErrorCode = xErrorCode(CONSTRAINT) | (4 << 8)
+	CONSTRAINT_NOTNULL      ExtendedErrorCode = xErrorCode(CONSTRAINT) | (5 << 8)
+	CONSTRAINT_PRIMARYKEY   ExtendedErrorCode = xErrorCode(CONSTRAINT) | (6 << 8)
+	CONSTRAINT_TRIGGER      ExtendedErrorCode = xErrorCode(CONSTRAINT) | (7 << 8)
+	CONSTRAINT_UNIQUE       ExtendedErrorCode = xErrorCode(CONSTRAINT) | (8 << 8)
+	CONSTRAINT_VTAB         ExtendedErrorCode = xErrorCode(CONSTRAINT) | (9 << 8)
+	CONSTRAINT_ROWID        ExtendedErrorCode = xErrorCode(CONSTRAINT) | (10 << 8)
+	CONSTRAINT_PINNED       ExtendedErrorCode = xErrorCode(CONSTRAINT) | (11 << 8)
+	CONSTRAINT_DATATYPE     ExtendedErrorCode = xErrorCode(CONSTRAINT) | (12 << 8)
+	NOTICE_RECOVER_WAL      ExtendedErrorCode = xErrorCode(NOTICE) | (1 << 8)
+	NOTICE_RECOVER_ROLLBACK ExtendedErrorCode = xErrorCode(NOTICE) | (2 << 8)
+	WARNING_AUTOINDEX       ExtendedErrorCode = xErrorCode(WARNING) | (1 << 8)
+	AUTH_USER               ExtendedErrorCode = xErrorCode(AUTH) | (1 << 8)
 )
 
 type OpenFlag uint32
@@ -160,7 +163,7 @@ const (
 	ACCESS_READ      AccessFlag = 2 /* Unused */
 )
 
-type PrepareFlag uint
+type PrepareFlag uint32
 
 const (
 	PREPARE_PERSISTENT PrepareFlag = 0x01
@@ -168,7 +171,7 @@ const (
 	PREPARE_NO_VTAB    PrepareFlag = 0x04
 )
 
-type Datatype uint
+type Datatype uint32
 
 const (
 	INTEGER Datatype = 1
diff --git a/vfs_unix.go b/vfs_unix.go
index 0d89108..d462e37 100644
--- a/vfs_unix.go
+++ b/vfs_unix.go
@@ -12,7 +12,7 @@ func deleteOnClose(f *os.File) {
 	_ = os.Remove(f.Name())
 }
 
-func (l *vfsFileLocker) GetShared() ExtendedErrorCode {
+func (l *vfsFileLocker) GetShared() xErrorCode {
 	// A PENDING lock is needed before acquiring a SHARED lock.
 	if err := l.fcntlSetLock(&syscall.Flock_t{
 		Type:  syscall.F_RDLCK,
@@ -40,7 +40,7 @@ func (l *vfsFileLocker) GetShared() ExtendedErrorCode {
 	return rc
 }
 
-func (l *vfsFileLocker) GetReserved() ExtendedErrorCode {
+func (l *vfsFileLocker) GetReserved() xErrorCode {
 	// Acquire the RESERVED lock.
 	return l.errorCode(l.fcntlSetLock(&syscall.Flock_t{
 		Type:  syscall.F_WRLCK,
@@ -49,7 +49,7 @@ func (l *vfsFileLocker) GetReserved() ExtendedErrorCode {
 	}), IOERR_LOCK)
 }
 
-func (l *vfsFileLocker) GetPending() ExtendedErrorCode {
+func (l *vfsFileLocker) GetPending() xErrorCode {
 	// Acquire the PENDING lock.
 	return l.errorCode(l.fcntlSetLock(&syscall.Flock_t{
 		Type:  syscall.F_WRLCK,
@@ -58,7 +58,7 @@ func (l *vfsFileLocker) GetPending() ExtendedErrorCode {
 	}), IOERR_LOCK)
 }
 
-func (l *vfsFileLocker) GetExclusive() ExtendedErrorCode {
+func (l *vfsFileLocker) GetExclusive() xErrorCode {
 	// Acquire the EXCLUSIVE lock.
 	return l.errorCode(l.fcntlSetLock(&syscall.Flock_t{
 		Type:  syscall.F_WRLCK,
@@ -67,7 +67,7 @@ func (l *vfsFileLocker) GetExclusive() ExtendedErrorCode {
 	}), IOERR_LOCK)
 }
 
-func (l *vfsFileLocker) Downgrade() ExtendedErrorCode {
+func (l *vfsFileLocker) Downgrade() xErrorCode {
 	// Downgrade to a SHARED lock.
 	if err := l.fcntlSetLock(&syscall.Flock_t{
 		Type:  syscall.F_RDLCK,
@@ -93,7 +93,7 @@ func (l *vfsFileLocker) Downgrade() ExtendedErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) Release() ExtendedErrorCode {
+func (l *vfsFileLocker) Release() xErrorCode {
 	// Release all locks.
 	if err := l.fcntlSetLock(&syscall.Flock_t{
 		Type: syscall.F_UNLCK,
@@ -103,7 +103,7 @@ func (l *vfsFileLocker) Release() ExtendedErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) CheckReserved() (bool, ExtendedErrorCode) {
+func (l *vfsFileLocker) CheckReserved() (bool, xErrorCode) {
 	// Test the RESERVED lock.
 	lock := syscall.Flock_t{
 		Type:  syscall.F_RDLCK,
@@ -142,7 +142,7 @@ func (l *vfsFileLocker) fcntlSetLock(lock *syscall.Flock_t) error {
 	return syscall.FcntlFlock(l.file.Fd(), F_SETLK, lock)
 }
 
-func (*vfsFileLocker) errorCode(err error, def ExtendedErrorCode) ExtendedErrorCode {
+func (*vfsFileLocker) errorCode(err error, def xErrorCode) xErrorCode {
 	if err == nil {
 		return _OK
 	}
@@ -155,9 +155,9 @@ func (*vfsFileLocker) errorCode(err error, def ExtendedErrorCode) ExtendedErrorC
 		case syscall.ENOLCK:
 		case syscall.EDEADLK:
 		case syscall.ETIMEDOUT:
-			return ExtendedErrorCode(BUSY)
+			return xErrorCode(BUSY)
 		case syscall.EPERM:
-			return ExtendedErrorCode(PERM)
+			return xErrorCode(PERM)
 		}
 	}
 	return def
diff --git a/vfs_windows.go b/vfs_windows.go
index d4cb3b2..3e0a277 100644
--- a/vfs_windows.go
+++ b/vfs_windows.go
@@ -4,30 +4,30 @@ import "os"
 
 func deleteOnClose(f *os.File) {}
 
-func (l *vfsFileLocker) GetShared() ExtendedErrorCode {
+func (l *vfsFileLocker) GetShared() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) GetReserved() ExtendedErrorCode {
+func (l *vfsFileLocker) GetReserved() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) GetPending() ExtendedErrorCode {
+func (l *vfsFileLocker) GetPending() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) GetExclusive() ExtendedErrorCode {
+func (l *vfsFileLocker) GetExclusive() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) Downgrade() ExtendedErrorCode {
+func (l *vfsFileLocker) Downgrade() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) Release() ExtendedErrorCode {
+func (l *vfsFileLocker) Release() xErrorCode {
 	return _OK
 }
 
-func (l *vfsFileLocker) CheckReserved() (bool, ExtendedErrorCode) {
+func (l *vfsFileLocker) CheckReserved() (bool, xErrorCode) {
 	return false, _OK
 }