diff --git a/example/glide_computer.cpp b/example/glide_computer.cpp
index 133a7713a..df2ca9093 100644
--- a/example/glide_computer.cpp
+++ b/example/glide_computer.cpp
@@ -163,7 +163,8 @@ void print(const aircraft_tow& tow)
 
 void example()
 {
-  using namespace mp_units::si::unit_symbols;
+  using mp_units::si::unit_symbols::m;
+  using mp_units::si::unit_symbols::s;
 
   const safety sfty = {300 * m};
   const auto gliders = get_gliders();
diff --git a/example/kalman_filter/kalman.h b/example/kalman_filter/kalman.h
index 06114cb03..f49d6f6c3 100644
--- a/example/kalman_filter/kalman.h
+++ b/example/kalman_filter/kalman.h
@@ -210,8 +210,8 @@ class MP_UNITS_STD_FMT::formatter<kalman::system_state<QPs...>, Char> {
   std::array<std::basic_string<Char>, sizeof...(QPs)> format_str_;
   std::tuple<MP_UNITS_STD_FMT::formatter<typename QPs::quantity_type, Char>...> formatters_{};
 
-  template<typename Formatter>
-  constexpr const Char* parse_default_spec(const Char* begin, const Char* end, Formatter& f, std::string& format_str)
+  template<std::forward_iterator It, typename Formatter>
+  constexpr It parse_default_spec(It begin, It end, Formatter& f, std::string& format_str)
   {
     if (begin == end || *begin++ != '[')
       throw MP_UNITS_STD_FMT::format_error("`default-spec` should contain a `[` character");
@@ -231,9 +231,8 @@ class MP_UNITS_STD_FMT::formatter<kalman::system_state<QPs...>, Char> {
     return ++it;  // skip `]`
   }
 
-  template<std::size_t... Is>
-  [[nodiscard]] constexpr const Char* parse_default_spec(const Char* begin, const Char* end, size_t idx,
-                                                         std::index_sequence<Is...>)
+  template<std::forward_iterator It, std::size_t... Is>
+  [[nodiscard]] constexpr It parse_default_spec(It begin, It end, size_t idx, std::index_sequence<Is...>)
   {
     auto parse = [&](bool flag, auto& f, std::basic_string<Char>& str) {
       return flag ? parse_default_spec(begin, end, f, str) : begin;
@@ -241,7 +240,8 @@ class MP_UNITS_STD_FMT::formatter<kalman::system_state<QPs...>, Char> {
     return std::max({parse(idx == Is, std::get<Is>(formatters_), format_str_[Is])...});
   }
 
-  [[nodiscard]] constexpr const Char* parse_defaults_specs(const Char* begin, const Char* end)
+  template<std::forward_iterator It>
+  [[nodiscard]] constexpr It parse_defaults_specs(It begin, It end)
   {
     if (begin == end || *begin == '}') return begin;
     if (*begin++ != ':') throw MP_UNITS_STD_FMT::format_error("`defaults-specs` should start with a `:`");
diff --git a/example/total_energy.cpp b/example/total_energy.cpp
index d65450873..82419760d 100644
--- a/example/total_energy.cpp
+++ b/example/total_energy.cpp
@@ -48,7 +48,10 @@ QuantityOf<isq::mechanical_energy> auto total_energy(QuantityOf<isq::momentum> a
 
 void si_example()
 {
-  using namespace mp_units::si::unit_symbols;
+  using mp_units::si::unit_symbols::kg;
+  using mp_units::si::unit_symbols::m;
+  using mp_units::si::unit_symbols::s;
+  using mp_units::si::unit_symbols::J;
   constexpr Unit auto GeV = si::giga<si::electronvolt>;
   constexpr quantity c = 1. * si::si2019::speed_of_light_in_vacuum;
   const quantity c2 = pow<2>(c);
diff --git a/example/unmanned_aerial_vehicle.cpp b/example/unmanned_aerial_vehicle.cpp
index 064e80553..4c5d2276e 100644
--- a/example/unmanned_aerial_vehicle.cpp
+++ b/example/unmanned_aerial_vehicle.cpp
@@ -70,6 +70,7 @@ constexpr const char* to_text(earth_gravity_model m)
       return "EGM2008-1";
   }
   assert(false && "unsupported enum value");
+  return nullptr;
 }
 
 template<earth_gravity_model M>
diff --git a/src/core/include/mp-units/bits/fmt.h b/src/core/include/mp-units/bits/fmt.h
index 92312bb1b..c01fb09f5 100644
--- a/src/core/include/mp-units/bits/fmt.h
+++ b/src/core/include/mp-units/bits/fmt.h
@@ -214,18 +214,18 @@ template<std::forward_iterator It>
 {
   MP_UNITS_EXPECTS(begin != end && '0' <= *begin && *begin <= '9');
   unsigned value = 0, prev = 0;
-  auto p = begin;
+  auto pos = begin;
   do {
     prev = value;
-    value = value * 10 + unsigned(*p - '0');
-    ++p;
-  } while (p != end && '0' <= *p && *p <= '9');
-  auto num_digits = p - begin;
-  begin = p;
+    value = value * 10 + unsigned(*pos - '0');
+    ++pos;
+  } while (pos != end && '0' <= *pos && *pos <= '9');
+  auto num_digits = pos - begin;
+  begin = pos;
   if (num_digits <= std::numeric_limits<int>::digits10) return static_cast<int>(value);
   // Check for overflow.
   const unsigned max = ::mp_units::detail::to_unsigned((std::numeric_limits<int>::max)());
-  return num_digits == std::numeric_limits<int>::digits10 + 1 && prev * 10ull + unsigned(p[-1] - '0') <= max
+  return num_digits == std::numeric_limits<int>::digits10 + 1 && prev * 10ull + unsigned(pos[-1] - '0') <= max
            ? static_cast<int>(value)
            : error_value;
 }
@@ -239,11 +239,11 @@ template<typename Char>
 template<std::forward_iterator It, typename Handler>
 [[nodiscard]] constexpr const It do_parse_arg_id(It begin, It end, Handler& handler)
 {
-  auto c = *begin;
-  if (c >= '0' && c <= '9') {
+  auto ch = *begin;
+  if (ch >= '0' && ch <= '9') {
     int index = 0;
     constexpr int max = (std::numeric_limits<int>::max)();
-    if (c != '0')
+    if (ch != '0')
       index = ::mp_units::detail::parse_nonnegative_int(begin, end, max);
     else
       ++begin;
@@ -252,8 +252,8 @@ template<std::forward_iterator It, typename Handler>
     handler.on_index(index);
     return begin;
   }
-  if (c == '%') return begin;  // mp-units extension
-  if (!::mp_units::detail::is_name_start(c)) {
+  if (ch == '%') return begin;  // mp-units extension
+  if (!::mp_units::detail::is_name_start(ch)) {
     MP_UNITS_THROW(MP_UNITS_STD_FMT::format_error("invalid format string"));
   }
   auto it = begin;
@@ -273,8 +273,8 @@ template<std::forward_iterator It, typename Handler>
 [[nodiscard]] constexpr It parse_arg_id(It begin, It end, Handler& handler)
 {
   MP_UNITS_EXPECTS(begin != end);
-  auto c = *begin;
-  if (c != '}' && c != ':') return ::mp_units::detail::do_parse_arg_id(begin, end, handler);
+  auto ch = *begin;
+  if (ch != '}' && ch != ':') return ::mp_units::detail::do_parse_arg_id(begin, end, handler);
   handler.on_auto();
   return begin;
 }
@@ -351,10 +351,10 @@ template<std::forward_iterator It, typename Specs>
 {
   MP_UNITS_EXPECTS(begin != end);
   auto align = fmt_align::none;
-  auto p = begin + code_point_length(begin);
-  if (end - p <= 0) p = begin;
+  auto pos = begin + code_point_length(begin);
+  if (end - pos <= 0) pos = begin;
   for (;;) {
-    switch (to_ascii(*p)) {
+    switch (to_ascii(*pos)) {
       case '<':
         align = fmt_align::left;
         break;
@@ -366,19 +366,19 @@ template<std::forward_iterator It, typename Specs>
         break;
     }
     if (align != fmt_align::none) {
-      if (p != begin) {
-        auto c = *begin;
-        if (c == '}') return begin;
-        if (c == '{') MP_UNITS_THROW(MP_UNITS_STD_FMT::format_error("invalid fill character '{'"));
-        specs.fill = {begin, p};
-        begin = p + 1;
+      if (pos != begin) {
+        auto ch = *begin;
+        if (ch == '}') return begin;
+        if (ch == '{') MP_UNITS_THROW(MP_UNITS_STD_FMT::format_error("invalid fill character '{'"));
+        specs.fill = {begin, pos};
+        begin = pos + 1;
       } else {
         ++begin;
       }
       break;
     }
-    if (p == begin) break;
-    p = begin;
+    if (pos == begin) break;
+    pos = begin;
   }
   if (align == fmt_align::none) align = default_align;  // mp-units extension
   specs.align = align;
diff --git a/src/core/include/mp-units/ext/fixed_string.h b/src/core/include/mp-units/ext/fixed_string.h
index f2155a060..050a2bacf 100644
--- a/src/core/include/mp-units/ext/fixed_string.h
+++ b/src/core/include/mp-units/ext/fixed_string.h
@@ -173,8 +173,8 @@ public:
   {
     CharT txt[N + N2];
     CharT* it = txt;
-    for (CharT c : lhs) *it++ = c;
-    for (CharT c : rhs) *it++ = c;
+    for (CharT ch : lhs) *it++ = ch;
+    for (CharT ch : rhs) *it++ = ch;
     return basic_fixed_string<CharT, N + N2>(txt, it);
   }
 
@@ -183,7 +183,7 @@ public:
   {
     CharT txt[N + 1];
     CharT* it = txt;
-    for (CharT c : lhs) *it++ = c;
+    for (CharT ch : lhs) *it++ = ch;
     *it++ = rhs;
     return basic_fixed_string<CharT, N + 1>(txt, it);
   }
@@ -194,7 +194,7 @@ public:
     CharT txt[1 + N];
     CharT* it = txt;
     *it++ = lhs;
-    for (CharT c : rhs) *it++ = c;
+    for (CharT ch : rhs) *it++ = ch;
     return basic_fixed_string<CharT, 1 + N>(txt, it);
   }
 
@@ -205,8 +205,8 @@ public:
     MP_UNITS_EXPECTS(rhs[N2 - 1] == CharT{});
     CharT txt[N + N2];
     CharT* it = txt;
-    for (CharT c : lhs) *it++ = c;
-    for (CharT c : rhs) *it++ = c;
+    for (CharT ch : lhs) *it++ = ch;
+    for (CharT ch : rhs) *it++ = ch;
     return txt;
   }
 
@@ -218,7 +218,7 @@ public:
     CharT txt[N1 + N];
     CharT* it = txt;
     for (std::size_t i = 0; i != N1 - 1; ++i) *it++ = lhs[i];
-    for (CharT c : rhs) *it++ = c;
+    for (CharT ch : rhs) *it++ = ch;
     *it++ = CharT();
     return txt;
   }
diff --git a/src/core/include/mp-units/framework/quantity.h b/src/core/include/mp-units/framework/quantity.h
index 379a0cdef..fec9e0a31 100644
--- a/src/core/include/mp-units/framework/quantity.h
+++ b/src/core/include/mp-units/framework/quantity.h
@@ -870,9 +870,9 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
         "`quantity-specs` should start with a `conversion-spec` ('%' characters expected)");
     auto ptr = begin;
     while (ptr != end) {
-      auto c = *ptr;
-      if (c == '}') break;
-      if (c == ':') {
+      auto ch = *ptr;
+      if (ch == '}') break;
+      if (ch == ':') {
         if (ptr + 1 != end && *(ptr + 1) == ':') {
           handler.on_text(begin, ++ptr);  // account for ':'
           ++ptr;                          // consume the second ':'
@@ -881,7 +881,7 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
         // default specs started
         break;
       }
-      if (c != '%') {
+      if (ch != '%') {
         ++ptr;
         continue;
       }
@@ -889,8 +889,8 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
       ++ptr;  // consume '%'
       if (ptr == end) throw MP_UNITS_STD_FMT::format_error("invalid `conversion-spec` format");
 
-      c = *ptr++;
-      switch (c) {
+      ch = *ptr++;
+      switch (ch) {
         case 'N':
           handler.on_number();
           break;
@@ -907,7 +907,7 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
           handler.on_text(ptr - 1, ptr);
           break;
         default:
-          throw MP_UNITS_STD_FMT::format_error(std::string("unknown `placement-type` token '") + c + "'");
+          throw MP_UNITS_STD_FMT::format_error(std::string("unknown `placement-type` token '") + ch + "'");
       }
       begin = ptr;
     }
@@ -942,9 +942,9 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
     if (begin == end || *begin == '}') return begin;
     if (*begin++ != ':') throw MP_UNITS_STD_FMT::format_error("`defaults-specs` should start with a `:`");
     do {
-      auto c = *begin++;
+      auto ch = *begin++;
       // TODO check if not repeated
-      switch (c) {
+      switch (ch) {
         case 'N':
           begin = parse_default_spec(begin, end, rep_formatter_, rep_format_str_);
           break;
@@ -955,7 +955,7 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
           begin = parse_default_spec(begin, end, dimension_formatter_, dimension_format_str_);
           break;
         default:
-          throw MP_UNITS_STD_FMT::format_error(std::string("unknown `subentity-id` token '") + c + "'");
+          throw MP_UNITS_STD_FMT::format_error(std::string("unknown `subentity-id` token '") + ch + "'");
       }
     } while (begin != end && *begin != '}');
     return begin;
diff --git a/src/core/include/mp-units/framework/quantity_spec.h b/src/core/include/mp-units/framework/quantity_spec.h
index 81b433770..166385e5f 100644
--- a/src/core/include/mp-units/framework/quantity_spec.h
+++ b/src/core/include/mp-units/framework/quantity_spec.h
@@ -1224,7 +1224,7 @@ template<QuantitySpec Q1, QuantitySpec Q2>
     // if quantities can't be converted in any direction check if they have a common base in the tree
     else if constexpr (detail::have_common_base(Q1{}, Q2{})) {
       constexpr auto base = detail::get_common_base(Q1{}, Q2{});
-      if constexpr (mp_units::implicitly_convertible(q1, base) && mp_units::implicitly_convertible(q2, base))
+      if constexpr (mp_units::implicitly_convertible(Q1{}, base) && mp_units::implicitly_convertible(Q2{}, base))
         return base;
       else
         return no_common_quantity_spec{};
diff --git a/src/core/include/mp-units/framework/value_cast.h b/src/core/include/mp-units/framework/value_cast.h
index 6a975cdfc..f342d664b 100644
--- a/src/core/include/mp-units/framework/value_cast.h
+++ b/src/core/include/mp-units/framework/value_cast.h
@@ -46,7 +46,7 @@ template<typename Rep, Unit UFrom, Unit UTo>
   else if constexpr (std::totally_ordered_with<Rep, std::uintmax_t> &&
                      requires(Rep v) { representation_values<Rep>::max(); }) {
     constexpr auto factor =
-      get_value<std::uintmax_t>(numerator(get_canonical_unit(from).mag / get_canonical_unit(to).mag));
+      get_value<std::uintmax_t>(numerator(get_canonical_unit(UFrom{}).mag / get_canonical_unit(UTo{}).mag));
     if constexpr (std::is_integral_v<Rep>)
       return !std::in_range<Rep>(factor);
     else