diff --git a/vfs_lock.go b/vfs_lock.go
index 8338372..2213224 100644
--- a/vfs_lock.go
+++ b/vfs_lock.go
@@ -172,8 +172,21 @@ func vfsUnlock(ctx context.Context, mod api.Module, pFile uint32, eLock vfsLockS
 
 func vfsCheckReservedLock(ctx context.Context, mod api.Module, pFile, pResOut uint32) uint32 {
 	file := vfsFile.GetOS(ctx, mod, pFile)
+	cLock := vfsFile.GetLock(ctx, mod, pFile)
+
+	// Connection state check.
+	if cLock < _NO_LOCK || cLock > _EXCLUSIVE_LOCK {
+		panic(assertErr())
+	}
+
+	var locked bool
+	var rc xErrorCode
+	if cLock >= _RESERVED_LOCK {
+		locked = true
+	} else {
+		locked, rc = vfsOS.CheckReservedLock(file)
+	}
 
-	locked, rc := vfsOS.CheckReservedLock(file)
 	var res uint32
 	if locked {
 		res = 1
diff --git a/vfs_lock_test.go b/vfs_lock_test.go
index 0b11512..cd2aa99 100644
--- a/vfs_lock_test.go
+++ b/vfs_lock_test.go
@@ -51,6 +51,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got != 0 {
 		t.Error("file was locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got != 0 {
+		t.Error("file was locked")
+	}
 
 	rc = vfsLock(ctx, mem.mod, pFile2, _SHARED_LOCK)
 	if rc != _OK {
@@ -64,6 +71,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got != 0 {
 		t.Error("file was locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got != 0 {
+		t.Error("file was locked")
+	}
 
 	rc = vfsLock(ctx, mem.mod, pFile2, _RESERVED_LOCK)
 	if rc != _OK {
@@ -81,6 +95,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got == 0 {
 		t.Error("file wasn't locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got == 0 {
+		t.Error("file wasn't locked")
+	}
 
 	rc = vfsLock(ctx, mem.mod, pFile2, _EXCLUSIVE_LOCK)
 	if rc != _OK {
@@ -94,6 +115,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got == 0 {
 		t.Error("file wasn't locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got == 0 {
+		t.Error("file wasn't locked")
+	}
 
 	rc = vfsLock(ctx, mem.mod, pFile1, _SHARED_LOCK)
 	if rc == _OK {
@@ -107,6 +135,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got == 0 {
 		t.Error("file wasn't locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got == 0 {
+		t.Error("file wasn't locked")
+	}
 
 	rc = vfsUnlock(ctx, mem.mod, pFile2, _SHARED_LOCK)
 	if rc != _OK {
@@ -120,6 +155,13 @@ func Test_vfsLock(t *testing.T) {
 	if got := mem.readUint32(pOutput); got != 0 {
 		t.Error("file was locked")
 	}
+	rc = vfsCheckReservedLock(ctx, mem.mod, pFile2, pOutput)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := mem.readUint32(pOutput); got != 0 {
+		t.Error("file was locked")
+	}
 
 	rc = vfsLock(ctx, mem.mod, pFile1, _SHARED_LOCK)
 	if rc != _OK {