From 0563b73fc0f1b30b2bfffbdb91487bdc7ec7bf4d Mon Sep 17 00:00:00 2001
From: esadomer <54475303+esadomer@users.noreply.github.com>
Date: Sat, 6 Jun 2026 18:22:12 +0300
Subject: [PATCH] gh-151021: Fix mmap empty searches past the end

---
 Lib/test/test_mmap.py                                          | 2 ++
 .../Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst     | 3 +++
 Modules/mmapmodule.c                                           | 2 --
 3 files changed, 5 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst

diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index 177fe45e8d97490..2e2ac147968dd4a 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -354,6 +354,8 @@ def test_find_end(self):
         self.assertEqual(m.find(b'one', 1, -1), 8)
         self.assertEqual(m.find(b'one', 1, -2), -1)
         self.assertEqual(m.find(bytearray(b'one')), 0)
+        self.assertEqual(m.find(b'', n + 1), -1)
+        self.assertEqual(m.rfind(b'', n + 1), -1)
 
         for i in range(-n-1, n+1):
             for j in range(-n-1, n+1):
diff --git a/Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst b/Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst
new file mode 100644
index 000000000000000..0617fa068c844d6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst
@@ -0,0 +1,3 @@
+Fix :meth:`mmap.mmap.find` and :meth:`~mmap.mmap.rfind` to return ``-1``
+when searching for an empty subsequence with a start position past the end
+of the mapping.
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index a30afe91f8fa171..6fb04ba7bd47c67 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -620,8 +620,6 @@ mmap_gfind_lock_held(mmap_object *self, Py_buffer *view, PyObject *start_obj,
         start += self->size;
     if (start < 0)
         start = 0;
-    else if (start > self->size)
-        start = self->size;
 
     if (end < 0)
         end += self->size;