diff --git a/src/_pytest/config/argparsing.py b/src/_pytest/config/argparsing.py
index 8fa33506b01..ddd24695095 100644
--- a/src/_pytest/config/argparsing.py
+++ b/src/_pytest/config/argparsing.py
@@ -44,7 +44,7 @@ def __init__(
         self._groups = []  # type: List[OptionGroup]
         self._processopt = processopt
         self._usage = usage
-        self._inidict = {}  # type: Dict[str, Tuple[str, Optional[str], Any]]
+        self._inidict = {}  # type: Dict[Optional[str], Tuple[str, Optional[str], Any]]
         self._ininames = []  # type: List[str]
         self.extra_info = {}  # type: Dict[str, Any]