diff --git a/buffet/string_utils.h b/buffet/string_utils.h
index bad62f3..3fad204 100644
--- a/buffet/string_utils.h
+++ b/buffet/string_utils.h
@@ -15,25 +15,25 @@
 // of original elements of the list.
 // By default, empty elements from the original string are omitted and
 // each element has all whitespaces trimmed off.
-std::vector<std::string> Split(std::string const& str,
+std::vector<std::string> Split(const std::string& str,
                                char delimiter,
                                bool trim_whitespaces = true,
                                bool purge_empty_strings = true);
 
 // Splits the string into two pieces at the first position of the specified
 // delimiter. By default, each part has all whitespaces trimmed off.
-std::pair<std::string, std::string> SplitAtFirst(std::string const& str,
+std::pair<std::string, std::string> SplitAtFirst(const std::string& str,
                                                  char delimiter,
                                                  bool trim_whitespaces = true);
 
 // Joins an array of strings into a single string separated by |delimiter|.
-std::string Join(char delimiter, std::vector<std::string> const& strings);
-std::string Join(std::string const& delimiter,
-                 std::vector<std::string> const& strings);
+std::string Join(char delimiter, const std::vector<std::string>& strings);
+std::string Join(const std::string& delimiter,
+                 const std::vector<std::string>& strings);
 std::string Join(char delimiter,
-                 std::string const& str1, std::string const& str2);
-std::string Join(std::string const& delimiter,
-                 std::string const& str1, std::string const& str2);
+                 const std::string& str1, const std::string& str2);
+std::string Join(const std::string& delimiter,
+                 const std::string& str1, const std::string& str2);
 
 } // namespace string_utils
 } // namespace chromeos