diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3f3ded06..6ee0a388 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@ Version 242:
 * test::stream has deprecated lowest_layer for ssl
 * MSVC uses ::fopen_s
 * Fix http::message constructor constraint
+* Check defined(BOOST_MSVC)
 
 --------------------------------------------------------------------------------
 
diff --git a/example/advanced/server-flex/advanced_server_flex.cpp b/example/advanced/server-flex/advanced_server_flex.cpp
index c65d3182..af2ada61 100644
--- a/example/advanced/server-flex/advanced_server_flex.cpp
+++ b/example/advanced/server-flex/advanced_server_flex.cpp
@@ -88,7 +88,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/advanced/server/advanced_server.cpp b/example/advanced/server/advanced_server.cpp
index 13be92ef..f1adbee6 100644
--- a/example/advanced/server/advanced_server.cpp
+++ b/example/advanced/server/advanced_server.cpp
@@ -83,7 +83,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/async-ssl/http_server_async_ssl.cpp b/example/http/server/async-ssl/http_server_async_ssl.cpp
index 3bb8a415..f51d445c 100644
--- a/example/http/server/async-ssl/http_server_async_ssl.cpp
+++ b/example/http/server/async-ssl/http_server_async_ssl.cpp
@@ -82,7 +82,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/async/http_server_async.cpp b/example/http/server/async/http_server_async.cpp
index 95493aa0..e02ec231 100644
--- a/example/http/server/async/http_server_async.cpp
+++ b/example/http/server/async/http_server_async.cpp
@@ -78,7 +78,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/coro-ssl/http_server_coro_ssl.cpp b/example/http/server/coro-ssl/http_server_coro_ssl.cpp
index 06f12603..d0c7e85e 100644
--- a/example/http/server/coro-ssl/http_server_coro_ssl.cpp
+++ b/example/http/server/coro-ssl/http_server_coro_ssl.cpp
@@ -81,7 +81,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/coro/http_server_coro.cpp b/example/http/server/coro/http_server_coro.cpp
index 6e75c54a..1c3f440b 100644
--- a/example/http/server/coro/http_server_coro.cpp
+++ b/example/http/server/coro/http_server_coro.cpp
@@ -78,7 +78,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/flex/http_server_flex.cpp b/example/http/server/flex/http_server_flex.cpp
index c4cac9fd..e535bdc4 100644
--- a/example/http/server/flex/http_server_flex.cpp
+++ b/example/http/server/flex/http_server_flex.cpp
@@ -81,7 +81,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/stackless-ssl/http_server_stackless_ssl.cpp b/example/http/server/stackless-ssl/http_server_stackless_ssl.cpp
index c05c66cb..17568d53 100644
--- a/example/http/server/stackless-ssl/http_server_stackless_ssl.cpp
+++ b/example/http/server/stackless-ssl/http_server_stackless_ssl.cpp
@@ -83,7 +83,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/stackless/http_server_stackless.cpp b/example/http/server/stackless/http_server_stackless.cpp
index 059ff934..eb17f4af 100644
--- a/example/http/server/stackless/http_server_stackless.cpp
+++ b/example/http/server/stackless/http_server_stackless.cpp
@@ -79,7 +79,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/sync-ssl/http_server_sync_ssl.cpp b/example/http/server/sync-ssl/http_server_sync_ssl.cpp
index 4fdd2d76..34b27753 100644
--- a/example/http/server/sync-ssl/http_server_sync_ssl.cpp
+++ b/example/http/server/sync-ssl/http_server_sync_ssl.cpp
@@ -80,7 +80,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/http/server/sync/http_server_sync.cpp b/example/http/server/sync/http_server_sync.cpp
index b6d49cdf..2c5ca60f 100644
--- a/example/http/server/sync/http_server_sync.cpp
+++ b/example/http/server/sync/http_server_sync.cpp
@@ -77,7 +77,7 @@ path_cat(
 	if (base.empty())
 		return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/example/websocket/server/chat-multi/http_session.cpp b/example/websocket/server/chat-multi/http_session.cpp
index 07921785..9d4dee87 100644
--- a/example/websocket/server/chat-multi/http_session.cpp
+++ b/example/websocket/server/chat-multi/http_session.cpp
@@ -62,7 +62,7 @@ path_cat(
     if(base.empty())
         return std::string(path);
     std::string result(base);
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     char constexpr path_separator = '\\';
     if(result.back() == path_separator)
         result.resize(result.size() - 1);
diff --git a/include/boost/beast/_experimental/unit_test/main.ipp b/include/boost/beast/_experimental/unit_test/main.ipp
index fa696940..0a4d4c55 100644
--- a/include/boost/beast/_experimental/unit_test/main.ipp
+++ b/include/boost/beast/_experimental/unit_test/main.ipp
@@ -38,7 +38,7 @@ int main(int ac, char const* av[])
     dstream log(std::cerr);
     std::unitbuf(log);
 
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
     {
         int flags = _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG);
         flags |= _CRTDBG_LEAK_CHECK_DF;
diff --git a/test/doc/http_snippets.cpp b/test/doc/http_snippets.cpp
index 3811514e..f7fc4e30 100644
--- a/test/doc/http_snippets.cpp
+++ b/test/doc/http_snippets.cpp
@@ -417,7 +417,7 @@ print(message<isRequest, Body, Fields> const& m)
 
 //]
 
-#if BOOST_MSVC
+#ifdef BOOST_MSVC
 //[http_snippet_16
 
 template<bool isRequest, class Body, class Fields>