diff --git a/toonz/sources/include/toonz/txshsimplelevel.h b/toonz/sources/include/toonz/txshsimplelevel.h
index 2ffba7e..d502ddb 100644
--- a/toonz/sources/include/toonz/txshsimplelevel.h
+++ b/toonz/sources/include/toonz/txshsimplelevel.h
@@ -302,6 +302,8 @@ The oldFp is used when the current scene path change...
   //! must have the same size).
   void renumber(const std::vector<TFrameId> &fids);
 
+  bool isFrameReadOnly(TFrameId fid);
+
 public:
   // Auxiliary files management: hooks, tpl, etc.
   // May throw; copy and rename perform touchparentdir
diff --git a/toonz/sources/tnztools/tool.cpp b/toonz/sources/tnztools/tool.cpp
index 8f8e641..a0c58d4 100644
--- a/toonz/sources/tnztools/tool.cpp
+++ b/toonz/sources/tnztools/tool.cpp
@@ -948,16 +948,10 @@ QString TTool::updateEnabled() {
     // Check TTool::ImageType tools
     if (toolType == TTool::LevelWriteTool) {
       // Check level against read-only status
-      if (sl->isReadOnly()) {
-        const std::set<TFrameId> &editableFrames = sl->getEditableRange();
-        TFrameId currentFid                      = getCurrentFid();
-
-        if (editableFrames.find(currentFid) == editableFrames.end())
-          return (
-              enable(false),
-              QObject::tr(
-                  "The current frame is locked: any editing is forbidden."));
-      }
+      if (sl->isFrameReadOnly(getCurrentFid()))
+        return (enable(false),
+                QObject::tr(
+                    "The current frame is locked: any editing is forbidden."));
 
       // Check level type write support
       if (sl->getPath().getType() ==
diff --git a/toonz/sources/toonz/filmstrip.cpp b/toonz/sources/toonz/filmstrip.cpp
index 301b8c5..69a9554 100644
--- a/toonz/sources/toonz/filmstrip.cpp
+++ b/toonz/sources/toonz/filmstrip.cpp
@@ -539,10 +539,6 @@ void FilmstripFrames::paintEvent(QPaintEvent *evt) {
 
   int frameCount = (int)fids.size();
 
-  std::set<TFrameId> editableFrameRange;
-
-  if (sl) editableFrameRange = sl->getEditableRange();
-
   bool isReadOnly    = false;
   if (sl) isReadOnly = sl->isReadOnly();
 
@@ -619,9 +615,7 @@ void FilmstripFrames::paintEvent(QPaintEvent *evt) {
 
       // Read-only frames (lock)
       if (0 <= i && i < frameCount) {
-        if ((editableFrameRange.empty() && isReadOnly) ||
-            (isReadOnly && (!editableFrameRange.empty() &&
-                            editableFrameRange.count(fids[i]) == 0))) {
+        if (sl->isFrameReadOnly(fids[i])) {
           static QPixmap lockPixmap(":Resources/forbidden.png");
           p.drawPixmap(tmp_frameRect.bottomLeft() + QPoint(3, -13), lockPixmap);
         }
diff --git a/toonz/sources/toonzlib/txshsimplelevel.cpp b/toonz/sources/toonzlib/txshsimplelevel.cpp
index e6f9886..c1c5a31 100644
--- a/toonz/sources/toonzlib/txshsimplelevel.cpp
+++ b/toonz/sources/toonzlib/txshsimplelevel.cpp
@@ -2251,3 +2251,24 @@ TRectD TXshSimpleLevel::getBBox(const TFrameId &fid) const {
   // Get the frame's dpi and traduce the bbox to inch coordinates
   return TScale(1.0 / dpiX, 1.0 / dpiY) * bbox;
 }
+
+bool TXshSimpleLevel::isFrameReadOnly(TFrameId fid) {
+  // For Raster and mesh files, check to see if files are marked as read-only at
+  // the OS level
+  if (getType() == OVL_XSHLEVEL || getType() == TZI_XSHLEVEL ||
+      getType() == MESH_XSHLEVEL) {
+    TFilePath fullPath = getScene()->decodeFilePath(m_path);
+    TFilePath path =
+        fullPath.getDots() == ".." ? fullPath.withFrame(fid) : fullPath;
+    if (!TSystem::doesExistFileOrLevel(path)) return false;
+    TFileStatus fs(path);
+    return !fs.isWritable();
+  }
+
+  // If Level is marked read only, check for editable frames
+  if (m_isReadOnly && !m_editableRange.empty() &&
+      m_editableRange.count(fid) != 0)
+    return false;
+
+  return m_isReadOnly;
+}