diff --git a/changelog/7872.doc.rst b/changelog/7872.doc.rst
new file mode 100644
index 000000000..46236acbf
--- /dev/null
+++ b/changelog/7872.doc.rst
@@ -0,0 +1 @@
+``_pytest.config.argparsing.Parser.addini()`` accepts explicit ``None`` and ``"string"``.
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 39fbe01a0..7e486e99e 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -1402,7 +1402,7 @@ class Config:
         elif type == "bool":
             return _strtobool(str(value).strip())
         else:
-            assert type is None
+            assert type in [None, "string"]
             return value
 
     def _getconftest_pathlist(
diff --git a/src/_pytest/config/argparsing.py b/src/_pytest/config/argparsing.py
index 86e9c990a..9a4819655 100644
--- a/src/_pytest/config/argparsing.py
+++ b/src/_pytest/config/argparsing.py
@@ -160,20 +160,23 @@ class Parser:
         self,
         name: str,
         help: str,
-        type: Optional["Literal['pathlist', 'args', 'linelist', 'bool']"] = None,
+        type: Optional[
+            "Literal['string', 'pathlist', 'args', 'linelist', 'bool']"
+        ] = None,
         default=None,
     ) -> None:
         """Register an ini-file option.
 
         :name: Name of the ini-variable.
-        :type: Type of the variable, can be ``pathlist``, ``args``, ``linelist``
-               or ``bool``.
+        :type: Type of the variable, can be ``string``, ``pathlist``, ``args``,
+               ``linelist`` or ``bool``.  Defaults to ``string`` if ``None`` or
+               not passed.
         :default: Default value if no ini-file option exists but is queried.
 
         The value of ini-variables can be retrieved via a call to
         :py:func:`config.getini(name) <_pytest.config.Config.getini>`.
         """
-        assert type in (None, "pathlist", "args", "linelist", "bool")
+        assert type in (None, "string", "pathlist", "args", "linelist", "bool")
         self._inidict[name] = (help, type, default)
         self._ininames.append(name)
 
diff --git a/testing/test_config.py b/testing/test_config.py
index 582d241a6..f3fa64372 100644
--- a/testing/test_config.py
+++ b/testing/test_config.py
@@ -570,11 +570,17 @@ class TestConfigAPI:
         assert pl[0] == tmpdir
         assert pl[1] == somepath
 
-    def test_addini(self, testdir):
+    @pytest.mark.parametrize("maybe_type", ["not passed", "None", '"string"'])
+    def test_addini(self, testdir, maybe_type):
+        if maybe_type == "not passed":
+            type_string = ""
+        else:
+            type_string = f", {maybe_type}"
+
         testdir.makeconftest(
-            """
+            f"""
             def pytest_addoption(parser):
-                parser.addini("myname", "my new ini value")
+                parser.addini("myname", "my new ini value"{type_string})
         """
         )
         testdir.makeini(