diff --git a/heudiconv/cli/run.py b/heudiconv/cli/run.py
index 42bc85d0..f149a1b9 100644
--- a/heudiconv/cli/run.py
+++ b/heudiconv/cli/run.py
@@ -4,6 +4,7 @@
 import os
 import sys
 from argparse import ArgumentParser
+from typing import Optional
 
 from .. import __version__
 from ..main import workflow
@@ -11,7 +12,7 @@
 lgr = logging.getLogger(__name__)
 
 
-def main(argv=None):
+def main(argv: Optional[list[str]] = None) -> None:
     parser = get_parser()
     args = parser.parse_args(argv)
     # exit if nothing to be done
@@ -24,7 +25,7 @@ def main(argv=None):
     workflow(**kwargs)
 
 
-def get_parser():
+def get_parser() -> ArgumentParser:
     docstr = ("""Example:
              heudiconv -d 'rawdata/{subject}' -o . -f heuristic.py -s s1 s2 s3""")
     parser = ArgumentParser(description=docstr)