diff --git a/README.md b/README.md
index c4ba326..e71da49 100644
--- a/README.md
+++ b/README.md
@@ -100,16 +100,21 @@ On BSD Unixes, this module uses
 [BSD locks](https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2).
 On BSD Unixes, BSD locks are fully compatible with POSIX advisory locks.
 
-On Windows, this module uses `LockFile`, `LockFileEx`, and `UnlockFile`,
+On Windows, this module uses `LockFileEx` and `UnlockFileEx`,
 like SQLite.
 
 On all other platforms, file locking is not supported, and you must use
 [`nolock=1`](https://sqlite.org/uri.html#urinolock)
+(or [`immutable=1`](https://sqlite.org/uri.html#uriimmutable))
 to open database files.
+
 To use the [`database/sql`](https://pkg.go.dev/database/sql) driver
 with `nolock=1` you must disable connection pooling by calling
 [`db.SetMaxOpenConns(1)`](https://pkg.go.dev/database/sql#DB.SetMaxOpenConns).
 
+You can use [`vfs.SupportsFileLocking`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs#SupportsFileLocking)
+to check if your platform supports file locking.
+
 ### Testing
 
 This project aims for [high test coverage](https://github.com/ncruces/go-sqlite3/wiki/Test-coverage-report).
diff --git a/vfs/os_nolock.go b/vfs/os_nolock.go
index d2beefb..82379ec 100644
--- a/vfs/os_nolock.go
+++ b/vfs/os_nolock.go
@@ -4,6 +4,14 @@ package vfs
 
 import "os"
 
+// SupportsFileLocking is false on platforms that do not support file locking.
+// To open a database file in one such platform,
+// you need to use the [nolock] or [immutable] URI parameters.
+//
+// [nolock]: https://sqlite.org/uri.html#urinolock
+// [immutable]: https://sqlite.org/uri.html#uriimmutable
+const SupportsFileLocking = false
+
 func osGetSharedLock(file *os.File) _ErrorCode {
 	return _IOERR_RDLOCK
 }
diff --git a/vfs/os_unix2.go b/vfs/os_unix_lock.go
similarity index 86%
rename from vfs/os_unix2.go
rename to vfs/os_unix_lock.go
index b57a032..9cbe152 100644
--- a/vfs/os_unix2.go
+++ b/vfs/os_unix_lock.go
@@ -9,6 +9,14 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// SupportsFileLocking is false on platforms that do not support file locking.
+// To open a database file in one such platform,
+// you need to use the [nolock] or [immutable] URI parameters.
+//
+// [nolock]: https://sqlite.org/uri.html#urinolock
+// [immutable]: https://sqlite.org/uri.html#uriimmutable
+const SupportsFileLocking = true
+
 func osGetSharedLock(file *os.File) _ErrorCode {
 	// Test the PENDING lock before acquiring a new SHARED lock.
 	if pending, _ := osCheckLock(file, _PENDING_BYTE, 1); pending {
diff --git a/vfs/os_windows.go b/vfs/os_windows.go
index b0d3c4d..7ea9775 100644
--- a/vfs/os_windows.go
+++ b/vfs/os_windows.go
@@ -9,6 +9,14 @@ import (
 	"golang.org/x/sys/windows"
 )
 
+// SupportsFileLocking is false on platforms that do not support file locking.
+// To open a database file in one such platform,
+// you need to use the [nolock] or [immutable] URI parameters.
+//
+// [nolock]: https://sqlite.org/uri.html#urinolock
+// [immutable]: https://sqlite.org/uri.html#uriimmutable
+const SupportsFileLocking = true
+
 func osGetSharedLock(file *os.File) _ErrorCode {
 	// Acquire the PENDING lock temporarily before acquiring a new SHARED lock.
 	rc := osReadLock(file, _PENDING_BYTE, 1, 0)
@@ -49,7 +57,7 @@ func osGetExclusiveLock(file *os.File) _ErrorCode {
 
 func osDowngradeLock(file *os.File, state LockLevel) _ErrorCode {
 	if state >= LOCK_EXCLUSIVE {
-		// Release the SHARED lock.
+		// Release the EXCLUSIVE lock.
 		osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
 
 		// Reacquire the SHARED lock.