From 041acf13440f9307dcc129eff21bcd065362ae91 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sun, 25 May 2025 15:00:47 +1000
Subject: [PATCH] Clear core image if memory mapping was used for last load

---
 Tests/test_tiff_crashes.py | 14 ++++++++++++++
 src/PIL/TiffImagePlugin.py |  5 +++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/Tests/test_tiff_crashes.py b/Tests/test_tiff_crashes.py
index 073e5415c..976f62384 100644
--- a/Tests/test_tiff_crashes.py
+++ b/Tests/test_tiff_crashes.py
@@ -52,3 +52,17 @@ def test_tiff_crashes(test_file: str) -> None:
         pytest.skip("test image not found")
     except OSError:
         pass
+
+
+def test_tiff_mmap() -> None:
+    try:
+        with Image.open("Tests/images/crash_mmap.tif") as im:
+            im.seek(1)
+            im.load()
+
+            im.seek(0)
+            im.load()
+    except FileNotFoundError:
+        if on_ci():
+            raise
+        pytest.skip("test image not found")
diff --git a/src/PIL/TiffImagePlugin.py b/src/PIL/TiffImagePlugin.py
index 88af9162e..5cbac0c26 100644
--- a/src/PIL/TiffImagePlugin.py
+++ b/src/PIL/TiffImagePlugin.py
@@ -1217,9 +1217,10 @@ class TiffImageFile(ImageFile.ImageFile):
             return
         self._seek(frame)
         if self._im is not None and (
-            self.im.size != self._tile_size or self.im.mode != self.mode
+            self.im.size != self._tile_size
+            or self.im.mode != self.mode
+            or self.readonly
         ):
-            # The core image will no longer be used
             self._im = None
 
     def _seek(self, frame: int) -> None: