From a7537b1b06490ef3dfbf0bf1c48a0b8c9aa36940 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sun, 30 Mar 2025 07:31:17 +1100
Subject: [PATCH] Only change readonly if saved filename matches opened
 filename

---
 Tests/test_image.py | 9 +++++++++
 src/PIL/Image.py    | 7 ++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/Tests/test_image.py b/Tests/test_image.py
index c2e850c36..7e6118d52 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -258,6 +258,15 @@ class TestImage:
             assert im.readonly
             im.save(temp_file)
 
+    def test_save_without_changing_readonly(self, tmp_path: Path) -> None:
+        temp_file = tmp_path / "temp.bmp"
+
+        with Image.open("Tests/images/rgb32bf-rgba.bmp") as im:
+            assert im.readonly
+
+            im.save(temp_file)
+            assert im.readonly
+
     def test_dump(self, tmp_path: Path) -> None:
         im = Image.new("L", (10, 10))
         im._dump(str(tmp_path / "temp_L.ppm"))
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 233df592c..c62d7a8a3 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2540,8 +2540,13 @@ class Image:
                 msg = f"unknown file extension: {ext}"
                 raise ValueError(msg) from e
 
+        from . import ImageFile
+
         # may mutate self!
-        self._ensure_mutable()
+        if isinstance(self, ImageFile.ImageFile) and filename == self.filename:
+            self._ensure_mutable()
+        else:
+            self.load()
 
         save_all = params.pop("save_all", None)
         self.encoderinfo = {**getattr(self, "encoderinfo", {}), **params}