diff --git a/sdks/python/apache_beam/transforms/window.py b/sdks/python/apache_beam/transforms/window.py
index a67e2cf1b50b..5bc047b48c7a 100644
--- a/sdks/python/apache_beam/transforms/window.py
+++ b/sdks/python/apache_beam/transforms/window.py
@@ -53,6 +53,7 @@
 
 from google.protobuf import duration_pb2
 from google.protobuf import timestamp_pb2
+from past.builtins import cmp
 
 from apache_beam.coders import coders
 from apache_beam.portability import common_urns
diff --git a/sdks/python/scripts/run_mini_py3lint.sh b/sdks/python/scripts/run_mini_py3lint.sh
index 63e71771d734..0729c7ba2cfc 100755
--- a/sdks/python/scripts/run_mini_py3lint.sh
+++ b/sdks/python/scripts/run_mini_py3lint.sh
@@ -48,5 +48,4 @@ if test $# -gt 0; then
 fi
 
 echo "Running flake8 for module $MODULE:"
-# TODO(BEAM-3959): Add F821 (undefined names) as soon as that test passes
-flake8 $MODULE --count --select=E9,F822,F823 --show-source --statistics
+flake8 $MODULE --count --select=E9,F821,F822,F823 --show-source --statistics