diff --git a/cli.py b/cli.py
index 6d581f32386a..7df68530ae29 100644
--- a/cli.py
+++ b/cli.py
@@ -1557,7 +1557,15 @@ def _setup_worktree(repo_root: str = None, sync_base: bool = True) -> Optional[D
     gitignore = Path(repo_root) / ".gitignore"
     _ignore_entry = ".worktrees/"
     try:
-        existing = gitignore.read_text() if gitignore.exists() else ""
+        # utf-8-sig: git files are UTF-8 and Notepad prepends a BOM, which
+        # would glue to the first line and defeat the membership check below
+        # (duplicating the entry); the locale default also breaks non-ASCII
+        # patterns on Windows. The append below already writes UTF-8.
+        existing = (
+            gitignore.read_text(encoding="utf-8-sig", errors="replace")
+            if gitignore.exists()
+            else ""
+        )
         if _ignore_entry not in existing.splitlines():
             with open(gitignore, "a", encoding="utf-8") as f:
                 if existing and not existing.endswith("\n"):
@@ -1607,7 +1615,14 @@ def _setup_worktree(repo_root: str = None, sync_base: bool = True) -> Optional[D
         try:
             repo_root_resolved = Path(repo_root).resolve()
             wt_path_resolved = wt_path.resolve()
-            for line in include_file.read_text().splitlines():
+            # utf-8-sig, not the locale default: on a cp1251/GBK Windows
+            # machine a UTF-8 include list either decodes to mojibake paths
+            # (entries silently not copied) or raises UnicodeDecodeError,
+            # which the enclosing handler swallows at DEBUG — no include is
+            # copied at all. A Notepad BOM likewise glued to the first entry.
+            for line in include_file.read_text(
+                encoding="utf-8-sig", errors="replace"
+            ).splitlines():
                 entry = line.strip()
                 if not entry or entry.startswith("#"):
                     continue
diff --git a/tests/cli/test_worktree_security.py b/tests/cli/test_worktree_security.py
index 73a242e0fdaa..bf2c2fa01b5e 100644
--- a/tests/cli/test_worktree_security.py
+++ b/tests/cli/test_worktree_security.py
@@ -128,3 +128,64 @@ class TestWorktreeIncludeSecurity:
             assert (linked_dir / "lib" / "marker.txt").read_text() == "venv marker"
         finally:
             _force_remove_worktree(info)
+
+
+class TestWorktreeIncludeEncoding:
+    """The include list and .gitignore are UTF-8 files; reading them with the
+    locale default breaks Windows (cp1251/GBK mojibake or UnicodeDecodeError,
+    swallowed at DEBUG so no include is copied), and a Notepad BOM glues to
+    the first line on every platform."""
+
+    def test_bom_in_worktreeinclude_does_not_hide_first_entry(self, git_repo):
+        import cli as cli_mod
+
+        (git_repo / ".env").write_text("SECRET=***\n")
+        # Notepad-style UTF-8 with BOM; the BOM must not become part of the
+        # first entry's path.
+        (git_repo / ".worktreeinclude").write_bytes(".env\n".encode("utf-8"))
+
+        info = None
+        try:
+            info = cli_mod._setup_worktree(str(git_repo))
+            assert info is not None
+            assert (Path(info["path"]) / ".env").exists()
+        finally:
+            _force_remove_worktree(info)
+
+    def test_non_ascii_worktreeinclude_entry_copied(self, git_repo):
+        import cli as cli_mod
+
+        secret = git_repo / "секреты.env"
+        secret.write_text("SECRET=***\n", encoding="utf-8")
+        (git_repo / ".worktreeinclude").write_bytes(
+            "# ключи агента\nсекреты.env\n".encode("utf-8")
+        )
+
+        info = None
+        try:
+            info = cli_mod._setup_worktree(str(git_repo))
+            assert info is not None
+            assert (Path(info["path"]) / "секреты.env").exists()
+        finally:
+            _force_remove_worktree(info)
+
+    def test_bom_in_gitignore_does_not_duplicate_worktrees_entry(self, git_repo):
+        import cli as cli_mod
+
+        (git_repo / ".gitignore").write_bytes(".worktrees/\n".encode("utf-8"))
+
+        info = None
+        try:
+            info = cli_mod._setup_worktree(str(git_repo))
+            assert info is not None
+            lines = (
+                (git_repo / ".gitignore")
+                .read_text(encoding="utf-8-sig")
+                .splitlines()
+            )
+            assert lines.count(".worktrees/") == 1, (
+                "BOM glued to the first line must not defeat the membership "
+                f"check and duplicate the entry: {lines!r}"
+            )
+        finally:
+            _force_remove_worktree(info)