diff --git a/changelog/13913.bugfix.rst b/changelog/13913.bugfix.rst
new file mode 100644
index 00000000000..a538c6518f9
--- /dev/null
+++ b/changelog/13913.bugfix.rst
@@ -0,0 +1 @@
+Fixed a regression where a conftest.py that registers command line options was sometimes not loaded as an initial conftest. This happened when a command line option's value was the path of an existing file (e.g. ``pytest --write-idents idents.txt``): due to intermixed argument parsing the value ended up among the positional arguments during pre-parsing and was treated as a test path, which suppressed the conftest discovery and made the option report as "unrecognized".
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 96b3dd6a86a..7ff2fc0b22a 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -650,10 +650,17 @@ def _set_initial_conftests(
             if not safe_exists(anchor):
                 continue
 
+            # With intermixed argument parsing, the path *value* of a command
+            # line option (e.g. ``--write-idents idents.txt``) can end up among
+            # the positional arguments. Such a file anchor must not prevent the
+            # conftest discovery for its directory (and its ``test*``
+            # sub-directories), otherwise conftests that register the option are
+            # not loaded as initial conftests and the option becomes
+            # "unrecognized" (#13913). Resolve file anchors to their directory.
+            anchor = self._get_directory(anchor)
             anchors.append(anchor)
             # Let's also consider test* subdirs.
-            if anchor.is_dir():
-                anchors.extend(x for x in anchor.glob("test*") if x.is_dir())
+            anchors.extend(x for x in anchor.glob("test*") if x.is_dir())
         if not anchors:
             anchors.append(invocation_dir)
             anchors.extend(x for x in invocation_dir.glob("test*") if x.is_dir())
diff --git a/testing/test_conftest.py b/testing/test_conftest.py
index 23a0db81c39..47d8baeeee6 100644
--- a/testing/test_conftest.py
+++ b/testing/test_conftest.py
@@ -462,6 +462,36 @@ def test_it(request):
     result.assert_outcomes(passed=1)
 
 
+def test_initial_conftest_loaded_when_option_value_is_existing_file(
+    pytester: Pytester,
+) -> None:
+    """An initial conftest registering a command line option is still loaded
+    when the option's value happens to be the path of an existing file.
+
+    With intermixed argument parsing, such a value ends up among the
+    positional arguments during pre-parsing and used to be treated as a test
+    path anchor, which suppressed the ``test*`` conftest discovery and left
+    the option "unrecognized". Regression test for #13913.
+    """
+    pytester.makepyfile(
+        **{
+            "tests/conftest.py": """
+                def pytest_addoption(parser):
+                    parser.addoption("--write-idents", action="store", default=None)
+            """,
+            "test_it.py": """
+                def test_it(request):
+                    assert request.config.getoption("--write-idents") == "idents.txt"
+            """,
+        }
+    )
+    # The option value is a path to an existing file on disk.
+    pytester.makefile(".txt", idents="")
+    result = pytester.runpytest("--write-idents", "idents.txt")
+    assert result.ret == ExitCode.OK
+    result.assert_outcomes(passed=1)
+
+
 def test_conftest_import_order(pytester: Pytester, monkeypatch: MonkeyPatch) -> None:
     ct1 = pytester.makeconftest("")
     sub = pytester.mkdir("sub")