diff --git a/vfs/api.go b/vfs/api.go
index e133e8b..3d4a2ad 100644
--- a/vfs/api.go
+++ b/vfs/api.go
@@ -171,5 +171,11 @@ type SharedMemory interface {
 	shmMap(context.Context, api.Module, int32, int32, bool) (uint32, _ErrorCode)
 	shmLock(int32, int32, _ShmFlag) _ErrorCode
 	shmUnmap(bool)
+	shmBarrier()
 	io.Closer
 }
+
+type blockingSharedMemory interface {
+	SharedMemory
+	shmEnableBlocking(block bool)
+}
diff --git a/vfs/shm.go b/vfs/shm.go
index 88306ef..c8163cd 100644
--- a/vfs/shm.go
+++ b/vfs/shm.go
@@ -6,6 +6,7 @@ import (
 	"context"
 	"io"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/ncruces/go-sqlite3/internal/util"
@@ -45,12 +46,15 @@ func NewSharedMemory(path string, flags OpenFlag) SharedMemory {
 	}
 }
 
+var _ blockingSharedMemory = &vfsShm{}
+
 type vfsShm struct {
 	*os.File
 	path     string
 	regions  []*util.MappedRegion
 	readOnly bool
 	blocking bool
+	sync.Mutex
 }
 
 func (s *vfsShm) shmOpen() _ErrorCode {
@@ -196,6 +200,11 @@ func (s *vfsShm) shmUnmap(delete bool) {
 	s.File = nil
 }
 
+func (s *vfsShm) shmBarrier() {
+	s.Lock()
+	s.Unlock()
+}
+
 func (s *vfsShm) shmEnableBlocking(block bool) {
 	s.blocking = block
 }
diff --git a/vfs/shm_bsd.go b/vfs/shm_bsd.go
index 8849cc7..dde90db 100644
--- a/vfs/shm_bsd.go
+++ b/vfs/shm_bsd.go
@@ -269,3 +269,8 @@ func (s *vfsShm) shmUnmap(delete bool) {
 	}
 	s.Close()
 }
+
+func (s *vfsShm) shmBarrier() {
+	s.lockMtx.Lock()
+	s.lockMtx.Unlock()
+}
diff --git a/vfs/vfs.go b/vfs/vfs.go
index eb606bf..8235490 100644
--- a/vfs/vfs.go
+++ b/vfs/vfs.go
@@ -5,7 +5,6 @@ import (
 	"crypto/rand"
 	"io"
 	"reflect"
-	"sync"
 	"time"
 
 	"github.com/ncruces/go-sqlite3/internal/util"
@@ -245,10 +244,9 @@ func vfsFileControl(ctx context.Context, mod api.Module, pFile uint32, op _Fcntl
 
 	case _FCNTL_LOCK_TIMEOUT:
 		if file, ok := file.(FileSharedMemory); ok {
-			if iface, ok := file.SharedMemory().(interface{ shmEnableBlocking(bool) }); ok {
-				if i := util.ReadUint32(mod, pArg); i == 0 || i == 1 {
-					iface.shmEnableBlocking(i != 0)
-				}
+			if shm, ok := file.SharedMemory().(blockingSharedMemory); ok {
+				shm.shmEnableBlocking(util.ReadUint32(mod, pArg) != 0)
+				return _OK
 			}
 		}
 
@@ -385,11 +383,9 @@ func vfsDeviceCharacteristics(ctx context.Context, mod api.Module, pFile uint32)
 	return file.DeviceCharacteristics()
 }
 
-var shmBarrier sync.Mutex
-
 func vfsShmBarrier(ctx context.Context, mod api.Module, pFile uint32) {
-	shmBarrier.Lock()
-	defer shmBarrier.Unlock()
+	shm := vfsFileGet(ctx, mod, pFile).(FileSharedMemory).SharedMemory()
+	shm.shmBarrier()
 }
 
 func vfsShmMap(ctx context.Context, mod api.Module, pFile uint32, iRegion, szRegion int32, bExtend, pp uint32) _ErrorCode {