diff --git a/src/core/include/mp-units/bits/external/fixed_string.h b/src/core/include/mp-units/bits/external/fixed_string.h
index 64e1172d..8eff4aa9 100644
--- a/src/core/include/mp-units/bits/external/fixed_string.h
+++ b/src/core/include/mp-units/bits/external/fixed_string.h
@@ -33,6 +33,7 @@
 #include <cstddef>
 #include <cstdlib>
 #include <ostream>
+#include <string_view>
 #endif
 
 MP_UNITS_EXPORT
@@ -60,34 +61,40 @@ struct basic_fixed_string {
 
   constexpr explicit(false) basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
   {
-    if constexpr (N != 0)
-      for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];
+    gsl_ExpectsAudit(txt[N] == CharT{});
+    for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];
+  }
+
+  template<std::input_iterator It, std::sentinel_for<It> S>
+    requires std::convertible_to<std::iter_value_t<It>, CharT>
+  constexpr explicit basic_fixed_string(It first, S last) noexcept
+  {
+    gsl_ExpectsAudit(std::distance(last, first) == N);
+    for (auto it = data_; first != last; ++first, ++it) *it = *first;
   }
 
   template<std::convertible_to<CharT>... Rest>
     requires(1 + sizeof...(Rest) == N)
-  constexpr explicit basic_fixed_string(CharT first, Rest... rest) noexcept : data_{first, rest..., CharT('\0')}
+  constexpr explicit basic_fixed_string(CharT first, Rest... rest) noexcept : data_{first, rest..., CharT{}}
   {
   }
 
-  constexpr basic_fixed_string(const CharT* ptr, std::integral_constant<std::size_t, N>) noexcept
-  {
-    if constexpr (N != 0)
-      for (std::size_t i = 0; i < N; ++i) data_[i] = *ptr++;
-  }
-
   [[nodiscard]] constexpr bool empty() const noexcept { return N == 0; }
   [[nodiscard]] constexpr size_type size() const noexcept { return N; }
   [[nodiscard]] constexpr const_pointer data() const noexcept { return data_; }
   [[nodiscard]] constexpr const CharT* c_str() const noexcept { return data(); }
-  [[nodiscard]] constexpr value_type operator[](size_type index) const noexcept { return data()[index]; }
+  [[nodiscard]] constexpr value_type operator[](size_type index) const noexcept
+  {
+    gsl_ExpectsAudit(index < N);
+    return data()[index];
+  }
 
   [[nodiscard]] constexpr const_iterator begin() const noexcept { return data(); }
   [[nodiscard]] constexpr const_iterator cbegin() const noexcept { return data(); }
   [[nodiscard]] constexpr const_iterator end() const noexcept { return data() + size(); }
   [[nodiscard]] constexpr const_iterator cend() const noexcept { return data() + size(); }
 
-  [[nodiscard]] constexpr std::basic_string_view<CharT> view() const noexcept
+  [[nodiscard]] constexpr operator std::basic_string_view<CharT>() const noexcept
   {
     return std::basic_string_view<CharT>(cbegin(), cend());
   }
@@ -104,11 +111,7 @@ struct basic_fixed_string {
     return basic_fixed_string<CharT, N + N2>(txt);
   }
 
-  [[nodiscard]] constexpr bool operator==(const basic_fixed_string& other) const
-  {
-    if (size() != other.size()) return false;
-    return detail::equal(begin(), end(), other.begin());  // TODO std::ranges::equal(*this, other)
-  }
+  [[nodiscard]] constexpr bool operator==(const basic_fixed_string&) const = default;
 
   template<std::size_t N2>
   [[nodiscard]] friend constexpr bool operator==(const basic_fixed_string&, const basic_fixed_string<CharT, N2>&)
@@ -138,22 +141,28 @@ basic_fixed_string(const CharT (&str)[N]) -> basic_fixed_string<CharT, N - 1>;
 template<typename CharT, std::convertible_to<CharT>... Rest>
 basic_fixed_string(CharT, Rest...) -> basic_fixed_string<CharT, 1 + sizeof...(Rest)>;
 
-template<typename CharT, std::size_t N>
-basic_fixed_string(const CharT* ptr, std::integral_constant<std::size_t, N>) -> basic_fixed_string<CharT, N>;
-
 template<std::size_t N>
 using fixed_string = basic_fixed_string<char, N>;
 
+template<std::size_t N>
+using fixed_wstring = basic_fixed_string<wchar_t, N>;
+
 template<std::size_t N>
 using fixed_u8string = basic_fixed_string<char8_t, N>;
 
+template<std::size_t N>
+using fixed_u16string = basic_fixed_string<char16_t, N>;
+
+template<std::size_t N>
+using fixed_u32string = basic_fixed_string<char32_t, N>;
+
 }  // namespace mp_units
 
 template<typename CharT, std::size_t N>
 struct MP_UNITS_STD_FMT::formatter<mp_units::basic_fixed_string<CharT, N>> : formatter<std::basic_string_view<CharT>> {
   template<typename FormatContext>
-  auto format(const mp_units::basic_fixed_string<CharT, N>& str, FormatContext& ctx)
+  auto format(const mp_units::basic_fixed_string<CharT, N>& str, FormatContext& ctx) const -> decltype(ctx.out())
   {
-    return formatter<std::basic_string_view<CharT>>::format(str.view(), ctx);
+    return formatter<std::basic_string_view<CharT>>::format(std::basic_string_view<CharT>(str), ctx);
   }
 };
diff --git a/src/core/include/mp-units/dimension.h b/src/core/include/mp-units/dimension.h
index bef17e10..25f032df 100644
--- a/src/core/include/mp-units/dimension.h
+++ b/src/core/include/mp-units/dimension.h
@@ -294,9 +294,9 @@ constexpr Out dimension_symbol_to(Out out, D d, dimension_symbol_formatting fmt
 namespace detail {
 
 template<typename CharT, std::size_t N, dimension_symbol_formatting fmt, Dimension D>
-[[nodiscard]] consteval std::array<CharT, N + 1> get_symbol_buffer(D)
+[[nodiscard]] consteval std::array<CharT, N> get_symbol_buffer(D)
 {
-  std::array<CharT, N + 1> buffer{};
+  std::array<CharT, N> buffer{};
   dimension_symbol_to<CharT>(buffer.begin(), D{}, fmt);
   return buffer;
 }
@@ -326,7 +326,7 @@ MP_UNITS_EXPORT template<dimension_symbol_formatting fmt = dimension_symbol_form
 #else
   constexpr std::size_t size = get_size();
   constexpr auto buffer = detail::get_symbol_buffer<CharT, size, fmt>(D{});
-  return basic_fixed_string(buffer.data(), std::integral_constant<std::size_t, size>{});
+  return basic_fixed_string<CharT, size>(buffer.begin(), buffer.end());
 #endif
 }
 
diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/unit.h
index 7ef58e03..6bcbd96a 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/unit.h
@@ -816,9 +816,9 @@ constexpr Out unit_symbol_to(Out out, U u, unit_symbol_formatting fmt = unit_sym
 namespace detail {
 
 template<typename CharT, std::size_t N, unit_symbol_formatting fmt, Unit U>
-[[nodiscard]] consteval std::array<CharT, N + 1> get_symbol_buffer(U)
+[[nodiscard]] consteval std::array<CharT, N> get_symbol_buffer(U)
 {
-  std::array<CharT, N + 1> buffer{};
+  std::array<CharT, N> buffer;
   unit_symbol_to<CharT>(buffer.begin(), U{}, fmt);
   return buffer;
 }
@@ -847,7 +847,7 @@ MP_UNITS_EXPORT template<unit_symbol_formatting fmt = unit_symbol_formatting{},
 #else
   constexpr std::size_t size = get_size();
   constexpr auto buffer = detail::get_symbol_buffer<CharT, size, fmt>(U{});
-  return basic_fixed_string(buffer.data(), std::integral_constant<std::size_t, size>{});
+  return basic_fixed_string<CharT, size>(buffer.begin(), buffer.end());
 #endif
 }
 
diff --git a/test/runtime/fmt_test.cpp b/test/runtime/fmt_test.cpp
index 5c1c0ad8..840cdda9 100644
--- a/test/runtime/fmt_test.cpp
+++ b/test/runtime/fmt_test.cpp
@@ -46,6 +46,18 @@ inline constexpr bool mp_units::is_vector<T> = true;
 using namespace mp_units;
 using namespace mp_units::si::unit_symbols;
 
+TEST_CASE("fixed_string", "[text][ostream][fmt]")
+{
+  basic_fixed_string txt = "units";
+  SECTION("iostream")
+  {
+    std::ostringstream os;
+    os << txt;
+    CHECK(os.str() == "units");
+  }
+  SECTION("fmt") { CHECK(MP_UNITS_STD_FMT::format("{}", txt) == "units"); }
+}
+
 TEST_CASE("operator<< on a quantity", "[text][ostream][fmt]")
 {
   std::ostringstream os;
diff --git a/test/static/fixed_string_test.cpp b/test/static/fixed_string_test.cpp
index a5d6769c..97f1c15f 100644
--- a/test/static/fixed_string_test.cpp
+++ b/test/static/fixed_string_test.cpp
@@ -30,6 +30,8 @@ constexpr basic_fixed_string txt1('a');
 static_assert(txt1.size() == 1);
 static_assert(txt1[0] == 'a');
 static_assert(txt1 == basic_fixed_string("a"));
+static_assert(txt1 != basic_fixed_string("b"));
+static_assert(txt1 != basic_fixed_string("aa"));
 static_assert(txt1 < basic_fixed_string("b"));
 static_assert(txt1 < basic_fixed_string("aa"));
 static_assert(txt1 + basic_fixed_string('b') == basic_fixed_string("ab"));
@@ -43,6 +45,8 @@ static_assert(txt2[0] == 'a');
 static_assert(txt2[1] == 'b');
 static_assert(txt2[2] == 'c');
 static_assert(txt2 == basic_fixed_string("abc"));
+static_assert(txt2 != basic_fixed_string("cba"));
+static_assert(txt2 != basic_fixed_string("abcd"));
 static_assert(txt2 < basic_fixed_string("b"));
 static_assert(txt2 > basic_fixed_string("aa"));
 static_assert(txt2 + basic_fixed_string('d') == basic_fixed_string("abcd"));
@@ -51,7 +55,7 @@ static_assert(txt2 + basic_fixed_string("def") == basic_fixed_string("abcdef"));
 static_assert(basic_fixed_string("def") + txt2 == basic_fixed_string("defabc"));
 
 #ifndef MP_UNITS_COMP_GCC
-static_assert(basic_fixed_string("abcd").view().find('c') == 2);
+static_assert(std::string_view(basic_fixed_string("abcd")).find('c') == 2);
 #endif
 
 }  // namespace