diff --git a/include/fast_float/fast_float.h b/include/fast_float/fast_float.h
index 8dfef02..7339847 100644
--- a/include/fast_float/fast_float.h
+++ b/include/fast_float/fast_float.h
@@ -34,7 +34,7 @@ template <typename T, typename UC = char,
           typename = FASTFLOAT_ENABLE_IF(is_supported_float_type<T>::value)>
 FASTFLOAT_CONSTEXPR20 from_chars_result_t<UC>
 from_chars(UC const *first, UC const *last, T &value,
-           chars_format fmt = chars_format::general) noexcept;
+           chars_format const fmt = chars_format::general) noexcept;
 
 /**
  * Like from_chars, but accepts an `options` argument to govern number parsing.
@@ -51,7 +51,7 @@ from_chars_advanced(UC const *first, UC const *last, T &value,
 template <typename T, typename UC = char,
           typename = FASTFLOAT_ENABLE_IF(is_supported_integer_type<T>::value)>
 FASTFLOAT_CONSTEXPR20 from_chars_result_t<UC>
-from_chars(UC const *first, UC const *last, T &value, int base = 10) noexcept;
+from_chars(UC const *first, UC const *last, T &value, int const base = 10) noexcept;
 
 } // namespace fast_float
 
diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index ce3a2d4..554b7cf 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -187,7 +187,7 @@ template <> struct from_chars_caller<std::float64_t> {
 template <typename T, typename UC, typename>
 FASTFLOAT_CONSTEXPR20 from_chars_result_t<UC>
 from_chars(UC const *first, UC const *last, T &value,
-           chars_format fmt /*= chars_format::general*/) noexcept {
+           chars_format const fmt /*= chars_format::general*/) noexcept {
   return from_chars_caller<T>::call(first, last, value,
                                     parse_options_t<UC>(fmt));
 }
@@ -350,7 +350,7 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
 
 template <typename T, typename UC, typename>
 FASTFLOAT_CONSTEXPR20 from_chars_result_t<UC>
-from_chars(UC const *first, UC const *last, T &value, int base) noexcept {
+from_chars(UC const *first, UC const *last, T &value, int const base) noexcept {
 
   static_assert(is_supported_integer_type<T>::value,
                 "only integer types are supported");