diff --git a/ci/pipeline/determine_tests_to_run.py b/ci/pipeline/determine_tests_to_run.py
index 942b0d87b..94cba857e 100644
--- a/ci/pipeline/determine_tests_to_run.py
+++ b/ci/pipeline/determine_tests_to_run.py
@@ -12,7 +12,8 @@ import subprocess
 import sys
 
 
-def list_changed_files(commit_range: str):
+# NOTE(simon): do not add type hint here because it's ran using python2 in CI.
+def list_changed_files(commit_range):
     """Returns a list of names of files changed in the given commit range.
 
     The function works by opening a subprocess and running git. If an error