diff --git a/cpplint.py b/cpplint.py
index dad86fe0d..3aa06b0e6 100755
--- a/cpplint.py
+++ b/cpplint.py
@@ -5433,7 +5433,7 @@ def CheckForIncludeWhatYouUse(filename, clean_lines, include_state, error,
 
   # include_dict is modified during iteration, so we iterate over a copy of
   # the keys.
-  header_keys = include_dict.keys()
+  header_keys = list(include_dict.keys())
   for header in header_keys:
     (same_module, common_path) = FilesBelongToSameModule(abs_filename, header)
     fullpath = common_path + header