diff --git a/include/boost/burl/detail/config.hpp b/include/boost/burl/detail/config.hpp
index 8212d1a..82fa64d 100644
--- a/include/boost/burl/detail/config.hpp
+++ b/include/boost/burl/detail/config.hpp
@@ -50,29 +50,6 @@ namespace burl
 #include <boost/config/auto_link.hpp>
 #endif
 
-//------------------------------------------------
-
-// Add source location to error codes
-#ifdef BOOST_BURL_NO_SOURCE_LOCATION
-#define BOOST_BURL_ERR(ev) (::boost::system::error_code(ev))
-#define BOOST_BURL_RETURN_EC(ev) return (ev)
-#else
-#define BOOST_BURL_ERR(ev)                                                     \
-    (::boost::system::error_code(                                              \
-        (ev),                                                                  \
-        []                                                                     \
-        {                                                                      \
-            static constexpr auto loc((BOOST_CURRENT_LOCATION));               \
-            return &loc;                                                       \
-        }()))
-#define BOOST_BURL_RETURN_EC(ev)                                               \
-    do                                                                         \
-    {                                                                          \
-        static constexpr auto loc##__LINE__((BOOST_CURRENT_LOCATION));         \
-        return ::boost::system::error_code((ev), &loc##__LINE__);              \
-    } while(0)
-#endif
-
 } // burl
 
 } // boost
diff --git a/include/boost/burl/head_parser.hpp b/include/boost/burl/head_parser.hpp
index c8984ae..3e14a50 100644
--- a/include/boost/burl/head_parser.hpp
+++ b/include/boost/burl/head_parser.hpp
@@ -15,7 +15,7 @@
 #include <boost/burl/response_head_base.hpp>
 
 #include <boost/http/error.hpp>
-#include <boost/system/error_code.hpp>
+#include <system_error>
 
 #include <cstdint>
 
@@ -259,7 +259,7 @@ class head_parser
     void
     parse(
         std::size_t n,
-        system::error_code& ec) noexcept;
+        std::error_code& ec) noexcept;
 
     /** Return the limits enforced by the parser.
 
@@ -402,13 +402,13 @@ class head_parser
     parse_start_line_(
         char const*& it,
         char const* end,
-        system::error_code& ec) noexcept;
+        std::error_code& ec) noexcept;
 
     void
     parse_fields_(
         char const*& it,
         char const* end,
-        system::error_code& ec) noexcept;
+        std::error_code& ec) noexcept;
 };
 
 } // namespace burl
diff --git a/include/boost/burl/message_reader.hpp b/include/boost/burl/message_reader.hpp
index 3fa6ef1..e5d6bca 100644
--- a/include/boost/burl/message_reader.hpp
+++ b/include/boost/burl/message_reader.hpp
@@ -268,7 +268,7 @@ read_header_(S& stream, parser& pr)
 {
     for(;;)
     {
-        system::error_code ec;
+        std::error_code ec;
         pr.parse_header(ec);
         if(!ec)
             co_return {};
@@ -286,7 +286,7 @@ read_body_(S& stream, parser& pr)
 {
     for(;;)
     {
-        system::error_code ec;
+        std::error_code ec;
         auto const sv = pr.flatten_body(ec);
         if(ec != http::error::need_data)
             co_return { std::error_code(ec), sv };
@@ -306,7 +306,7 @@ read_some_(
 {
     for(;;)
     {
-        system::error_code ec;
+        std::error_code ec;
         auto const n = pr.read_some(buffers, ec);
         if(ec != http::error::need_data)
             co_return { std::error_code(ec), n };
@@ -365,7 +365,7 @@ pull_(
 {
     for(;;)
     {
-        system::error_code ec;
+        std::error_code ec;
         auto const bufs = pr.pull(dest, ec);
         if(ec != http::error::need_data)
             co_return { std::error_code(ec), bufs };
diff --git a/include/boost/burl/message_writer.hpp b/include/boost/burl/message_writer.hpp
index 2054aef..61fdc03 100644
--- a/include/boost/burl/message_writer.hpp
+++ b/include/boost/burl/message_writer.hpp
@@ -261,7 +261,7 @@ drive_(
     std::size_t total = 0;
     for(;;)
     {
-        system::error_code ec;
+        std::error_code ec;
         auto const body = bp.data();
         auto const bufs = sr.frame(
             dest, body, more || bp.more(), ec);
diff --git a/include/boost/burl/parser.hpp b/include/boost/burl/parser.hpp
index ded6fda..657baa2 100644
--- a/include/boost/burl/parser.hpp
+++ b/include/boost/burl/parser.hpp
@@ -19,7 +19,6 @@
 
 #include <boost/capy/buffers.hpp>
 #include <boost/http/metadata.hpp>
-#include <boost/system/error_code.hpp>
 
 #include <array>
 #include <cstddef>
@@ -346,7 +345,7 @@ class parser
     */
     BOOST_BURL_DECL
     void
-    parse_header(system::error_code& ec);
+    parse_header(std::error_code& ec);
 
     /** Flatten the body in place and return it.
 
@@ -373,7 +372,7 @@ class parser
     */
     BOOST_BURL_DECL
     std::string_view
-    flatten_body(system::error_code& ec);
+    flatten_body(std::error_code& ec);
 
     /** Copy body octets into caller-supplied memory.
 
@@ -397,7 +396,7 @@ class parser
     std::size_t
     read_some(
         MB const& buffers,
-        system::error_code& ec);
+        std::error_code& ec);
 
     /** Return available body octets in place.
 
@@ -424,7 +423,7 @@ class parser
     std::span<capy::const_buffer>
     pull(
         std::span<capy::const_buffer> dest,
-        system::error_code& ec);
+        std::error_code& ec);
 
     /** Release body octets returned by @ref pull.
 
@@ -464,7 +463,7 @@ class parser
     void
     parse_trailer(
         fields_base& f,
-        system::error_code& ec);
+        std::error_code& ec);
 
 protected:
     parser() = default;
@@ -522,12 +521,12 @@ class parser
     std::size_t
     read_some_(
         capy::mutable_buffer dest,
-        system::error_code& ec);
+        std::error_code& ec);
 
     std::size_t
     decode_some_(
         capy::mutable_buffer dest,
-        system::error_code& ec);
+        std::error_code& ec);
 
     std::unique_ptr<char[]> buf_;
     head_parser hp_;
@@ -556,7 +555,7 @@ std::size_t
 parser::
 read_some(
     MB const& buffers,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     std::size_t n = 0;
     auto const end = capy::end(buffers);
diff --git a/include/boost/burl/serializer.hpp b/include/boost/burl/serializer.hpp
index 4ca29d1..6a0a3ca 100644
--- a/include/boost/burl/serializer.hpp
+++ b/include/boost/burl/serializer.hpp
@@ -17,7 +17,6 @@
 
 #include <boost/assert.hpp>
 #include <boost/capy/buffers.hpp>
-#include <boost/system/error_code.hpp>
 
 #include <cstddef>
 #include <cstdint>
@@ -467,7 +466,7 @@ class serializer
         std::span<capy::const_buffer> dest,
         CB const& buffers,
         bool more,
-        system::error_code& ec)
+        std::error_code& ec)
     {
         source_of<CB> src(buffers);
         return frame_(dest, src, more, ec);
@@ -496,7 +495,7 @@ class serializer
     frame(
         std::span<capy::const_buffer> dest,
         bool more,
-        system::error_code& ec)
+        std::error_code& ec)
     {
         source src;
         return frame_(dest, src, more, ec);
@@ -586,7 +585,7 @@ class serializer
         std::span<capy::const_buffer> dest,
         source& src,
         bool more,
-        system::error_code& ec);
+        std::error_code& ec);
 
     bool
     chunked_() const noexcept;
@@ -620,13 +619,13 @@ class serializer
     void
     encode_(
         source& src,
-        system::error_code& ec);
+        std::error_code& ec);
 
     bool
     ingest_(
         source& src,
         bool more,
-        system::error_code& ec);
+        std::error_code& ec);
 
     std::span<capy::const_buffer const>
     gather_(
diff --git a/include/boost/burl/test/response_factory.hpp b/include/boost/burl/test/response_factory.hpp
index d4bf377..57d4aa0 100644
--- a/include/boost/burl/test/response_factory.hpp
+++ b/include/boost/burl/test/response_factory.hpp
@@ -276,7 +276,7 @@ class response_factory
         {
             if(auto [ec] = co_await message_reader{
                 &conn, &parser }.read_header(); ec)
-                throw system::system_error(ec);
+                throw std::system_error(ec);
         }());
 
         return response{
diff --git a/src/detail/grammar.hpp b/src/detail/grammar.hpp
index daddb1e..037e6d6 100644
--- a/src/detail/grammar.hpp
+++ b/src/detail/grammar.hpp
@@ -13,7 +13,7 @@
 
 #include <boost/config.hpp>
 #include <boost/http/error.hpp>
-#include <boost/system/error_code.hpp>
+#include <system_error>
 
 #include <cstddef>
 #include <string_view>
@@ -123,7 +123,7 @@ parse_token_to_eol(
     char const* it,
     char const* end,
     char const*& token_end,
-    system::error_code& ec) noexcept
+    std::error_code& ec) noexcept
 {
     for(;; ++it)
     {
@@ -175,7 +175,7 @@ parse_field(
     char const* end,
     std::string_view& name,
     std::string_view& value,
-    system::error_code& ec)
+    std::error_code& ec)
 {
 /*  header-field    = field-name ":" OWS field-value OWS
 
@@ -253,7 +253,7 @@ parse_limited(
     char const* end,
     std::size_t limit,
     http::error limit_err,
-    system::error_code& ec) noexcept
+    std::error_code& ec) noexcept
 {
     bool const limited = [&]()
     {
diff --git a/src/head_parser.cpp b/src/head_parser.cpp
index c3bd477..608e572 100644
--- a/src/head_parser.cpp
+++ b/src/head_parser.cpp
@@ -59,7 +59,7 @@ parse_method(
     char const*& it,
     char const* end,
     std::string_view& result,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     // parse token SP
     auto const first = it;
@@ -92,7 +92,7 @@ parse_target(
     char const*& it,
     char const* end,
     std::string_view& result,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     // parse target SP
     auto const first = it;
@@ -125,7 +125,7 @@ parse_version(
     char const*& it,
     char const* end,
     version& result,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     if(distance(it, end) < 8)
     {
@@ -152,7 +152,7 @@ parse_status(
     char const*& it,
     char const* end,
     std::uint16_t& result,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     // parse 3(digit) SP
     if(distance(it, end) < 4)
@@ -193,7 +193,7 @@ parse_reason(
     char const*& it,
     char const* end,
     std::string_view& result,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     auto const first = it;
     char const* token_end = nullptr;
@@ -309,7 +309,7 @@ void
 head_parser::
 parse(
     std::size_t n,
-    system::error_code& ec) noexcept
+    std::error_code& ec) noexcept
 {
     ec.clear();
     auto const& h  = h_();
@@ -369,7 +369,7 @@ head_parser::
 parse_start_line_(
     char const*& it,
     char const* end,
-    system::error_code& ec) noexcept
+    std::error_code& ec) noexcept
 {
     auto& h = h_();
     auto const first = it;
@@ -454,7 +454,7 @@ head_parser::
 parse_fields_(
     char const*& it,
     char const* end,
-    system::error_code& ec) noexcept
+    std::error_code& ec) noexcept
 {
     auto& h = h_();
     std::string_view name;
diff --git a/src/parser.cpp b/src/parser.cpp
index 6d20ad5..8a211a6 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -577,7 +577,7 @@ flatten_chunks_()
 
 void
 parser::
-parse_header(system::error_code& ec)
+parse_header(std::error_code& ec)
 {
     BOOST_ASSERT(started_);
 
@@ -672,7 +672,7 @@ set_body_limit(std::uint64_t n) noexcept
 
 std::string_view
 parser::
-flatten_body(system::error_code& ec)
+flatten_body(std::error_code& ec)
 {
     parse_header(ec);
     if(ec)
@@ -765,7 +765,7 @@ std::size_t
 parser::
 decode_some_(
     capy::mutable_buffer dest,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     if(dest.size() == 0)
         return 0;
@@ -861,7 +861,7 @@ std::size_t
 parser::
 read_some_(
     capy::mutable_buffer dest,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     parse_header(ec);
     if(ec)
@@ -975,7 +975,7 @@ std::span<capy::const_buffer>
 parser::
 pull(
     std::span<capy::const_buffer> dest,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     parse_header(ec);
     if(ec)
@@ -1109,7 +1109,7 @@ void
 parser::
 parse_trailer(
     fields_base& f,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     ec = {};
 
diff --git a/src/serializer.cpp b/src/serializer.cpp
index d4c58c8..65b2a99 100644
--- a/src/serializer.cpp
+++ b/src/serializer.cpp
@@ -255,7 +255,7 @@ decide_framing_(std::uint64_t total) noexcept
 
 void
 serializer::
-encode_(source& src, system::error_code& ec)
+encode_(source& src, std::error_code& ec)
 {
     auto feed = [&](
         capy::const_buffer in, bool more)
@@ -285,7 +285,7 @@ encode_(source& src, system::error_code& ec)
             return;
         auto const more = !sealed_ || src.remain != 0;
         stage_.consume(feed(stage_.data(), more));
-        if(ec.failed() || !enc_)
+        if(ec || !enc_)
             return;
     }
 
@@ -298,7 +298,7 @@ encode_(source& src, system::error_code& ec)
             cur, !sealed_ || src.remain != 0);
         cur += n;
         input_digested_ += n;
-        if(ec.failed() || !enc_)
+        if(ec || !enc_)
             return;
         if(cur.size() == 0)
             cur = src.next();
@@ -310,7 +310,7 @@ encode_(source& src, system::error_code& ec)
         if(enc_out_.capacity() == 0)
             return;
         feed({}, false);
-        if(ec.failed() || !enc_)
+        if(ec || !enc_)
             return;
     }
 }
@@ -320,7 +320,7 @@ serializer::
 ingest_(
     source& src,
     bool more,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     auto const sealing = !more && !sealed_;
 
@@ -495,7 +495,7 @@ frame_(
     std::span<capy::const_buffer> dest,
     source& src,
     bool more,
-    system::error_code& ec)
+    std::error_code& ec)
 {
     BOOST_ASSERT(msg_ != nullptr);
 
diff --git a/test/unit/head_parser.cpp b/test/unit/head_parser.cpp
index 1f38082..01900c0 100644
--- a/test/unit/head_parser.cpp
+++ b/test/unit/head_parser.cpp
@@ -75,7 +75,7 @@ class head_parser_test
     // place s at the parse base past the `size`
     // bytes already there, then parse the new total
     static
-    system::error_code
+    std::error_code
     feed(
         head_parser& pr,
         std::size_t& size,
@@ -85,14 +85,14 @@ class head_parser_test
         BOOST_ASSERT(base + size + s.size() <= pr.ceiling());
         std::memcpy(base + size, s.data(), s.size());
         size += s.size();
-        system::error_code ec;
+        std::error_code ec;
         pr.parse(size, ec);
         return ec;
     }
 
     // one shot into a parser with nothing in it yet
     static
-    system::error_code
+    std::error_code
     feed(
         head_parser& pr,
         std::string_view s)
@@ -121,7 +121,7 @@ class head_parser_test
         std::memcpy(buf_, msg.data(), msg.size());
         std::memcpy(buf_ + msg.size(), body.data(), body.size());
         auto const fed = msg.size() + body.size();
-        system::error_code ec;
+        std::error_code ec;
         pr.parse(fed, ec);
         BOOST_TEST(!ec);
 
@@ -186,7 +186,7 @@ class head_parser_test
             "\r\n";
 
         head_parser pr(true, buf_, sizeof(buf_));
-        system::error_code ec;
+        std::error_code ec;
         std::size_t n = 0;
         for(char const c : msg)
         {
@@ -417,7 +417,7 @@ class head_parser_test
                 "\r\n";
 
             head_parser pr(true, buf_, sizeof(buf_));
-            system::error_code ec;
+            std::error_code ec;
             // bytes are appended one at a time;
             // those already parsed are resolved in
             // place and never rewritten
@@ -593,7 +593,7 @@ class head_parser_test
         {
             head_parser pr(is_request, buf_, sizeof(buf_), limits);
             std::size_t n = 0;
-            system::error_code ec = feed(pr, n, msg);
+            std::error_code ec = feed(pr, n, msg);
             BOOST_TEST(ec == e);
             // errors are sticky
             pr.parse(n, ec);
@@ -888,7 +888,7 @@ class head_parser_test
             {
                 head_parser pr(
                     true, buf_, sizeof(buf_), limits);
-                system::error_code ec;
+                std::error_code ec;
                 for(std::size_t n = 0;; ++n)
                 {
                     pr.parse(n, ec);
@@ -982,7 +982,7 @@ class head_parser_test
 
         head_parser pr(true, tiny, sizeof(tiny));
         BOOST_TEST(pr.ceiling() == tiny); // default max_fields = 100
-        system::error_code ec;
+        std::error_code ec;
         pr.parse(0, ec);
         BOOST_TEST(ec == http::error::in_place_overflow);
         // the error is derived again on request
@@ -1055,7 +1055,7 @@ class head_parser_test
         // limits with it
         header_limits const lim{ .max_fields = 4 };
         head_parser pr(true, buf, sizeof(buf), lim);
-        system::error_code ec;
+        std::error_code ec;
         std::size_t n = 0;
         std::memcpy(buf, msg.data(), 21);
         n = 21;
@@ -1149,7 +1149,7 @@ class head_parser_test
         std::memmove(buf, lo.data(), lo.size());
         pr.reset(buf);
         n = lo.size();
-        system::error_code ec;
+        std::error_code ec;
         pr.parse(n, ec);
         BOOST_TEST(! ec);
         BOOST_TEST_EQ(pr.request_head().target(), "/b");
@@ -1185,7 +1185,7 @@ class head_parser_test
             {
                 head_parser pr(true, raw, n, lim);
                 BOOST_TEST(pr.ceiling() == raw);
-                system::error_code ec;
+                std::error_code ec;
                 pr.parse(0, ec);
                 BOOST_TEST(ec == http::error::in_place_overflow);
             }
@@ -1212,7 +1212,7 @@ class head_parser_test
     // bytes or the caller has none left to give. Reports
     // how much was placed.
     static
-    system::error_code
+    std::error_code
     drive(
         head_parser& pr,
         std::string_view s,
@@ -1220,7 +1220,7 @@ class head_parser_test
         std::size_t& fed)
     {
         auto* const base = base_of(pr);
-        system::error_code ec;
+        std::error_code ec;
         fed = 0;
         for(;;)
         {
@@ -1294,7 +1294,7 @@ class head_parser_test
                 if(off + n > sizeof(raw))
                     continue;
 
-                system::error_code first;
+                std::error_code first;
                 for(std::size_t chunk : { 0u, 1u, 7u })
                 {
                     std::memset(raw, 0xCD, sizeof(raw));
@@ -1680,7 +1680,7 @@ class head_parser_test
         int done = 0;
         for(int round = 0; round < 4; ++round)
         {
-            system::error_code ec;
+            std::error_code ec;
             for(;;)
             {
                 pr.parse(held, ec);
diff --git a/test/unit/parser.cpp b/test/unit/parser.cpp
index cd545f8..03a9ede 100644
--- a/test/unit/parser.cpp
+++ b/test/unit/parser.cpp
@@ -170,7 +170,7 @@ struct test_parser : parser
     {
         for(;;)
         {
-            system::error_code ec;
+            std::error_code ec;
             parse_header(ec);
             if(ec != http::error::need_data)
                 return ec;
@@ -187,7 +187,7 @@ struct test_parser : parser
 
         for(;;)
         {
-            system::error_code ec;
+            std::error_code ec;
             auto const sv = flatten_body(ec);
             if(ec != http::error::need_data)
                 return { ec, sv };
@@ -205,7 +205,7 @@ struct test_parser : parser
 
         for(;;)
         {
-            system::error_code ec;
+            std::error_code ec;
             auto const n = parser::read_some(buffers, ec);
             if(ec != http::error::need_data)
                 return { ec, n };
@@ -252,7 +252,7 @@ struct test_parser : parser
 
         for(;;)
         {
-            system::error_code ec;
+            std::error_code ec;
             auto const bufs = parser::pull(dest, ec);
             if(ec != http::error::need_data)
                 return { ec, bufs };
@@ -552,7 +552,7 @@ class parser_test
         pr.start();
         for(int i = 0; i != 5; ++i)
         {
-            system::error_code ec;
+            std::error_code ec;
             pr.parse_header(ec);
             BOOST_TEST(ec == http::error::need_data);
             BOOST_TEST(!pr.got_header());
@@ -1217,7 +1217,7 @@ class parser_test
         BOOST_TEST(pr.has_buffered_data());
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 3u);
@@ -1261,7 +1261,7 @@ class parser_test
         BOOST_TEST(body == "hello world");
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 1u);
@@ -1305,7 +1305,7 @@ class parser_test
             BOOST_TEST(!ec);
             BOOST_TEST(pr.got_body());
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(tec == http::error::incomplete);
             BOOST_TEST_EQ(f.size(), 0u);
@@ -1329,7 +1329,7 @@ class parser_test
         BOOST_TEST(got == "abc");
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 1u);
@@ -1355,7 +1355,7 @@ class parser_test
             BOOST_TEST(!pr.has_buffered_data());
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(!tec);
             BOOST_TEST(f.empty());
@@ -1375,7 +1375,7 @@ class parser_test
             BOOST_TEST(body == "hello");
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(!tec);
             BOOST_TEST(f.empty());
@@ -1401,7 +1401,7 @@ class parser_test
         BOOST_TEST(!ec);
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 2u);
@@ -1438,7 +1438,7 @@ class parser_test
         BOOST_TEST(body == "hello");
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 2u);
@@ -1472,7 +1472,7 @@ class parser_test
             BOOST_TEST(!ec);
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             if(over)
             {
@@ -1512,7 +1512,7 @@ class parser_test
             BOOST_TEST(pr.got_body());
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(tec == http::error::bad_field_name);
             BOOST_TEST_EQ(f.size(), 1u);
@@ -1541,7 +1541,7 @@ class parser_test
             BOOST_TEST(!ec);
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(tec == http::error::bad_line_ending);
             BOOST_TEST(f.empty());
@@ -1568,7 +1568,7 @@ class parser_test
         // the trailer remains available for a retry
         char small[8];
         static_fields sf(small, sizeof(small));
-        system::error_code tec;
+        std::error_code tec;
         BOOST_TEST_THROWS(
             pr.parse_trailer(sf, tec), std::length_error);
 
@@ -1650,7 +1650,7 @@ class parser_test
             }
 
             fields f;
-            system::error_code tec;
+            std::error_code tec;
             pr.parse_trailer(f, tec);
             BOOST_TEST(!tec);
             BOOST_TEST_EQ(f.size(), 1u);
@@ -3377,7 +3377,7 @@ class parser_test
         BOOST_TEST(pr.got_body());
 
         fields f;
-        system::error_code tec;
+        std::error_code tec;
         pr.parse_trailer(f, tec);
         BOOST_TEST(!tec);
         BOOST_TEST_EQ(f.size(), 1u);
diff --git a/test/unit/request_head.cpp b/test/unit/request_head.cpp
index 2ee2a74..0a3806a 100644
--- a/test/unit/request_head.cpp
+++ b/test/unit/request_head.cpp
@@ -1060,7 +1060,7 @@ class request_head_test
             [&](head_parser& pr)
             {
                 std::memcpy(buf, msg.data(), msg.size());
-                system::error_code ec;
+                std::error_code ec;
                 pr.parse(msg.size(), ec);
                 BOOST_TEST(!ec);
             };
diff --git a/test/unit/request_parser.cpp b/test/unit/request_parser.cpp
index 6a6d03f..12460ff 100644
--- a/test/unit/request_parser.cpp
+++ b/test/unit/request_parser.cpp
@@ -52,7 +52,7 @@ class request_parser_test
             "\r\n"
             "hello");
 
-        system::error_code ec;
+        std::error_code ec;
         pr.parse_header(ec);
         BOOST_TEST(!ec);
         BOOST_TEST(pr.got_header());
diff --git a/test/unit/response_head.cpp b/test/unit/response_head.cpp
index 87da62e..65171c4 100644
--- a/test/unit/response_head.cpp
+++ b/test/unit/response_head.cpp
@@ -474,7 +474,7 @@ class response_head_test
             [&](head_parser& pr)
             {
                 std::memcpy(buf, msg.data(), msg.size());
-                system::error_code ec;
+                std::error_code ec;
                 pr.parse(msg.size(), ec);
                 BOOST_TEST(!ec);
             };
@@ -523,7 +523,7 @@ class response_head_test
             "\r\n";
         head_parser pr(false, buf, sizeof(buf));
         std::memcpy(buf, msg.data(), msg.size());
-        system::error_code ec;
+        std::error_code ec;
         pr.parse(msg.size(), ec);
         BOOST_TEST(!ec);
         response_head_base const& base = pr.response_head();
diff --git a/test/unit/response_parser.cpp b/test/unit/response_parser.cpp
index 7d62c58..83dab01 100644
--- a/test/unit/response_parser.cpp
+++ b/test/unit/response_parser.cpp
@@ -51,7 +51,7 @@ class response_parser_test
             "\r\n"
             "hello");
 
-        system::error_code ec;
+        std::error_code ec;
         pr.parse_header(ec);
         BOOST_TEST(!ec);
         BOOST_TEST(pr.got_header());
@@ -88,7 +88,7 @@ class response_parser_test
             "Content-Length: 5\r\n"
             "\r\n");
 
-        system::error_code ec;
+        std::error_code ec;
         pr.parse_header(ec);
         BOOST_TEST(!ec);
         BOOST_TEST(pr.got_header());
diff --git a/test/unit/serializer.cpp b/test/unit/serializer.cpp
index 660ad3f..0ebd8d0 100644
--- a/test/unit/serializer.cpp
+++ b/test/unit/serializer.cpp
@@ -151,7 +151,7 @@ class serializer_test
     // `wire`, consuming at most `step` octets per lap so every
     // cursor split point is exercised when `step` is small.
     // Returns when frame() has no work for this input.
-    static system::error_code
+    static std::error_code
     drive(
         serializer& sr,
         std::string& wire,
@@ -163,7 +163,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 body.data(), body.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, more, ec);
             if(bufs.empty())
@@ -186,7 +186,7 @@ class serializer_test
 
     // Writes the whole of `body` without ending the message;
     // the sans-I/O equivalent of the awaitable write().
-    static system::error_code
+    static std::error_code
     write(
         serializer& sr,
         std::string& wire,
@@ -204,7 +204,7 @@ class serializer_test
 
     // Ends the body with `body`; the sans-I/O equivalent of the
     // awaitable write_eof().
-    static system::error_code
+    static std::error_code
     write_eof(
         serializer& sr,
         std::string& wire,
@@ -222,7 +222,7 @@ class serializer_test
 
     // Flushes outstanding output (and the header) without
     // supplying anything; the sans-I/O drain().
-    static system::error_code
+    static std::error_code
     drain(
         serializer& sr,
         std::string& wire,
@@ -234,7 +234,7 @@ class serializer_test
 
     // The same, through the frame() overload that takes no
     // buffer sequence at all.
-    static system::error_code
+    static std::error_code
     drain_bufferless(
         serializer& sr,
         std::string& wire,
@@ -242,7 +242,7 @@ class serializer_test
     {
         for(;;)
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, more, ec);
             if(bufs.empty())
@@ -314,7 +314,7 @@ class serializer_test
             capy::make_buffer(b2) };
 
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const out = sr.frame(dest, bufs, false, ec);
         BOOST_TEST(!ec);
@@ -750,7 +750,7 @@ class serializer_test
         std::string_view rem(body);
         capy::const_buffer const b{
             rem.data(), rem.size() };
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
 
         auto out = sr.frame(dest, b, true, ec);
@@ -795,7 +795,7 @@ class serializer_test
             body.data(), body.size() };
         auto const flatten = [&]
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, true, ec);
             BOOST_TEST(!ec);
@@ -835,7 +835,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 rem.data(), rem.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, true, ec);
             BOOST_TEST(!ec);
@@ -885,7 +885,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 rem.data(), rem.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, true, ec);
             BOOST_TEST(!ec);
@@ -932,7 +932,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 body.data(), body.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, true, ec);
             BOOST_TEST(!ec);
@@ -993,7 +993,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 rem.data(), rem.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const bufs = sr.frame(dest, b, true, ec);
             BOOST_TEST(!ec);
@@ -1033,7 +1033,7 @@ class serializer_test
         sr.start(&req);
 
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[32];
         auto const out = sr.frame(dest, bufs, false, ec);
         BOOST_TEST(!ec);
@@ -1074,7 +1074,7 @@ class serializer_test
         {
             capy::const_buffer const b{
                 rem.data(), rem.size() };
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[1];
             auto const bufs = sr.frame(dest, b, more, ec);
             more = false;
@@ -1118,7 +1118,7 @@ class serializer_test
             {
                 capy::const_buffer const b{
                     rem2.data(), rem2.size() };
-                system::error_code ec;
+                std::error_code ec;
                 capy::const_buffer dest[1];
                 auto const bufs = sr2.frame(dest, b, false, ec);
                 BOOST_TEST(!ec);
@@ -1169,7 +1169,7 @@ class serializer_test
         // the wire takes the header, the prefix, and ten octets
         std::string wire;
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             auto const out = sr.frame(dest, true, ec);
             BOOST_TEST(!ec);
@@ -1230,7 +1230,7 @@ class serializer_test
         // for all forty octets; the wire takes the prefix and
         // ten of them
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             capy::const_buffer const b{
                 rem.data(), rem.size() };
@@ -1258,7 +1258,7 @@ class serializer_test
         // fewer than the chunk still owes
         while(!sr.is_done())
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             capy::const_buffer const b{ rem.data(),
                 (std::min)(std::size_t(10), rem.size()) };
@@ -1300,7 +1300,7 @@ class serializer_test
         sr.start(&req);
 
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[32];
         auto const out = sr.frame(dest, bufs, false, ec);
         BOOST_TEST(!ec);
@@ -1348,7 +1348,7 @@ class serializer_test
         BOOST_TEST(sr.should_drain());
 
         capy::const_buffer const b{ "def", 3 };
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const bufs = sr.frame(dest, b, true, ec);
         BOOST_TEST(!ec);
@@ -1480,7 +1480,7 @@ class serializer_test
         std::string wire;
         std::string_view rem(body);
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             capy::const_buffer const b{
                 rem.data(), rem.size() };
@@ -1659,7 +1659,7 @@ class serializer_test
             std::string const b = make_body(10);
             {
                 // declare eof; the wire takes nothing
-                system::error_code ec;
+                std::error_code ec;
                 capy::const_buffer dest[dest_n];
                 capy::const_buffer const cb{
                     b.data(), b.size() };
@@ -1700,7 +1700,7 @@ class serializer_test
         sr.start(&res);
 
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
 
         // the wire takes half the header
         {
@@ -1765,7 +1765,7 @@ class serializer_test
 
             std::string_view body("hello");
             {
-                system::error_code ec;
+                std::error_code ec;
                 capy::const_buffer const cb{
                     body.data(), body.size() };
                 BOOST_TEST(
@@ -1800,7 +1800,7 @@ class serializer_test
             // the empty-dest call opens the chunk covering the
             // staged and the supplied octets
             {
-                system::error_code ec;
+                std::error_code ec;
                 capy::const_buffer const cb{
                     body.data() + 2, 3 };
                 BOOST_TEST(
@@ -1824,7 +1824,7 @@ class serializer_test
             sr.start(&res);
 
             {
-                system::error_code ec;
+                std::error_code ec;
                 BOOST_TEST(sr.frame({}, false, ec).empty());
                 BOOST_TEST(!ec);
                 BOOST_TEST_EQ(sr.consume(0), 0u);
@@ -1870,7 +1870,7 @@ class serializer_test
         // chunk stands as debt
         std::string_view body("hello");
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             capy::const_buffer const cb{
                 body.data(), body.size() };
@@ -1882,7 +1882,7 @@ class serializer_test
         // prefix is accepted, the surplus is not — and no error
         // yet
         {
-            system::error_code ec;
+            std::error_code ec;
             capy::const_buffer dest[dest_n];
             std::string_view rem("helloworld");
             capy::const_buffer const cb{
@@ -2562,7 +2562,7 @@ class serializer_test
         serializer sr(cfg);
         sr.start(&req, &enc);
 
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         capy::const_buffer const b{
             body.data(), body.size() };
@@ -2839,7 +2839,7 @@ class serializer_test
             capy::make_buffer(b2) };
 
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const out = sr.frame(dest, bufs, false, ec);
         BOOST_TEST(!ec);
@@ -2877,7 +2877,7 @@ class serializer_test
         capy::const_buffer const b{
             body.data(), body.size() };
         std::string wire;
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const out = sr.frame(dest, b, true, ec);
         BOOST_TEST(!ec);
@@ -2918,7 +2918,7 @@ class serializer_test
         // fill the encoder's output; 64 == 0x40
         capy::const_buffer const b{
             body1.data(), body1.size() };
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const out = sr.frame(dest, b, true, ec);
         BOOST_TEST(!ec);
@@ -3071,7 +3071,7 @@ class serializer_test
 
         capy::const_buffer const b{
             body.data(), body.size() };
-        system::error_code ec;
+        std::error_code ec;
         capy::const_buffer dest[dest_n];
         auto const out = sr.frame(dest, b, true, ec);
         BOOST_TEST(!out.empty());