diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index a6e05e75ff1e9..8bbde3dc6a22c 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -3278,7 +3278,7 @@ def _CheckCrbugLinksHaveHttps(input_api, output_api):
   """Checks that crbug(.com) links are correctly prefixed by https://,
    unless they come in the accepted form TODO(crbug.com/...)
   """
-  white_list = r'.+%s' % _IMPLEMENTATION_EXTENSIONS
+  white_list = (r'.+%s' % _IMPLEMENTATION_EXTENSIONS, )
   black_list = (_EXCLUDED_PATHS + _TEST_CODE_EXCLUDED_PATHS)
   sources = lambda f: input_api.FilterSourceFile(
       f, white_list=white_list, black_list=black_list)
diff --git a/PRESUBMIT_test_mocks.py b/PRESUBMIT_test_mocks.py
index 3b491d963ed2c..ed6a750de3238 100644
--- a/PRESUBMIT_test_mocks.py
+++ b/PRESUBMIT_test_mocks.py
@@ -94,12 +94,16 @@ def FilterSourceFile(self, file, white_list=(), black_list=()):
     local_path = file.LocalPath()
     found_in_white_list = not white_list
     if white_list:
+      if type(white_list) is str:
+        raise TypeError('white_list should be an iterable of strings')
       for pattern in white_list:
         compiled_pattern = re.compile(pattern)
         if compiled_pattern.search(local_path):
           found_in_white_list = True
           break
     if black_list:
+      if type(black_list) is str:
+        raise TypeError('black_list should be an iterable of strings')
       for pattern in black_list:
         compiled_pattern = re.compile(pattern)
         if compiled_pattern.search(local_path):