diff --git a/solver/llbsolver/file/backend.go b/solver/llbsolver/file/backend.go
index 2c8bb23e5..2f8c4183c 100644
--- a/solver/llbsolver/file/backend.go
+++ b/solver/llbsolver/file/backend.go
@@ -211,8 +211,16 @@ func docopy(ctx context.Context, src, dest string, action pb.FileActionCopy, u *
 	return nil
 }
 
+// NewFileOpBackend returns a new file operation backend. The executor is currently only used for Windows,
+// and it is used to construct the readUserFn field set in the returned Backend.
+func NewFileOpBackend(exec executor.Executor) *Backend {
+	return &Backend{
+		readUserFn: getReadUserFn(exec),
+	}
+}
+
 type Backend struct {
-	Executor executor.Executor
+	readUserFn func(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error)
 }
 
 func (fb *Backend) Mkdir(ctx context.Context, m, user, group fileoptypes.Mount, action pb.FileActionMkDir) error {
@@ -228,7 +236,8 @@ func (fb *Backend) Mkdir(ctx context.Context, m, user, group fileoptypes.Mount,
 	}
 	defer lm.Unmount()
 
-	u, err := readUser(action.Owner, user, group, fb.Executor)
+	// u, err := readUser(action.Owner, user, group, fb.Executor)
+	u, err := fb.readUserFn(action.Owner, user, group)
 	if err != nil {
 		return err
 	}
@@ -249,7 +258,7 @@ func (fb *Backend) Mkfile(ctx context.Context, m, user, group fileoptypes.Mount,
 	}
 	defer lm.Unmount()
 
-	u, err := readUser(action.Owner, user, group, fb.Executor)
+	u, err := fb.readUserFn(action.Owner, user, group)
 	if err != nil {
 		return err
 	}
@@ -297,7 +306,7 @@ func (fb *Backend) Copy(ctx context.Context, m1, m2, user, group fileoptypes.Mou
 	}
 	defer lm2.Unmount()
 
-	u, err := readUser(action.Owner, user, group, fb.Executor)
+	u, err := fb.readUserFn(action.Owner, user, group)
 	if err != nil {
 		return err
 	}
diff --git a/solver/llbsolver/file/user_linux.go b/solver/llbsolver/file/user_linux.go
index 1d2970ce9..d204f80a4 100644
--- a/solver/llbsolver/file/user_linux.go
+++ b/solver/llbsolver/file/user_linux.go
@@ -14,7 +14,11 @@ import (
 	copy "github.com/tonistiigi/fsutil/copy"
 )
 
-func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
+func getReadUserFn(exec executor.Executor) func(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+	return readUser
+}
+
+func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
 	if chopt == nil {
 		return nil, nil
 	}
diff --git a/solver/llbsolver/file/user_other.go b/solver/llbsolver/file/user_other.go
index 34f6e8d2d..9e97afce3 100644
--- a/solver/llbsolver/file/user_other.go
+++ b/solver/llbsolver/file/user_other.go
@@ -11,7 +11,11 @@ import (
 	copy "github.com/tonistiigi/fsutil/copy"
 )
 
-func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
+func getReadUserFn(exec executor.Executor) func(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+	return readUser
+}
+
+func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
 	if chopt == nil {
 		return nil, nil
 	}
diff --git a/solver/llbsolver/file/user_windows.go b/solver/llbsolver/file/user_windows.go
index d0eb76b57..10b938b65 100644
--- a/solver/llbsolver/file/user_windows.go
+++ b/solver/llbsolver/file/user_windows.go
@@ -12,6 +12,12 @@ import (
 	copy "github.com/tonistiigi/fsutil/copy"
 )
 
+func getReadUserFn(exec executor.Executor) func(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+	return func(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+		return readUser(chopt, mu, mg, exec)
+	}
+}
+
 func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
 	if chopt == nil {
 		return nil, nil
diff --git a/solver/llbsolver/ops/file.go b/solver/llbsolver/ops/file.go
index 128fffbe2..179c167b5 100644
--- a/solver/llbsolver/ops/file.go
+++ b/solver/llbsolver/ops/file.go
@@ -167,7 +167,9 @@ func (f *fileOp) Exec(ctx context.Context, g session.Group, inputs []solver.Resu
 		inpRefs = append(inpRefs, workerRef.ImmutableRef)
 	}
 
-	fs := NewFileOpSolver(f.w, &file.Backend{Executor: f.w.Executor()}, f.refManager)
+	backend := file.NewFileOpBackend(f.w.Executor())
+
+	fs := NewFileOpSolver(f.w, backend, f.refManager)
 	outs, err := fs.Solve(ctx, inpRefs, f.op.Actions, g)
 	if err != nil {
 		return nil, err