diff --git a/mount/mount.go b/mount/mount.go
index 24bfc7d01..ae7520f98 100644
--- a/mount/mount.go
+++ b/mount/mount.go
@@ -68,6 +68,17 @@ func UnmountMounts(mounts []Mount, target string, flags int) error {
 	return nil
 }
 
+// ReadOnly returns a boolean value indicating whether this mount has the "ro"
+// option set.
+func (m *Mount) ReadOnly() bool {
+	for _, option := range m.Options {
+		if option == "ro" {
+			return true
+		}
+	}
+	return false
+}
+
 // Mount to the provided target path.
 func (m *Mount) Mount(target string) error {
 	target, err := fs.RootPath(target, m.Target)
diff --git a/mount/mount_windows.go b/mount/mount_windows.go
index e7d5a5113..b86ba0d7a 100644
--- a/mount/mount_windows.go
+++ b/mount/mount_windows.go
@@ -38,15 +38,6 @@ var (
 	ErrNotImplementOnWindows = errors.New("not implemented under windows")
 )
 
-func (m *Mount) ReadOnly() bool {
-	for _, option := range m.Options {
-		if option == "ro" {
-			return true
-		}
-	}
-	return false
-}
-
 // Mount to the provided target.
 func (m *Mount) mount(target string) (retErr error) {
 	if m.Type != "windows-layer" {