diff --git a/src/ocrmypdf/cli.py b/src/ocrmypdf/cli.py
index 6d8d4296..24d5e036 100644
--- a/src/ocrmypdf/cli.py
+++ b/src/ocrmypdf/cli.py
@@ -6,12 +6,15 @@
 
 
 import argparse
+from typing import Optional, Type, TypeVar
 
 from ocrmypdf._version import PROGRAM_NAME as _PROGRAM_NAME
 from ocrmypdf._version import __version__ as _VERSION
 
+T = TypeVar('T')
 
-def numeric(basetype, min_=None, max_=None):
+
+def numeric(basetype: Type[T], min_: Optional[T] = None, max_: Optional[T] = None):
     """Validator for numeric params"""
     min_ = basetype(min_) if min_ is not None else None
     max_ = basetype(max_) if max_ is not None else None