diff --git a/CLAUDE.md b/CLAUDE.md
index 912365a4..c14dd921 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -60,3 +60,21 @@ T default_value();
 - Concise, dry answers
 - Full files, not diffs
 - Accurate, compiling C++ code
+
+## Symbol Visibility
+
+- Mark **all public classes with virtual functions or virtual base classes** with  
+  `BOOST_HTTP_PROTO_SYMBOL_VISIBLE`.
+
+  - This is required for:
+    - DSO (Dynamic Shared Object) builds compiled with hidden visibility.
+    - DLL builds with MinGW GCC due to its [non-conformance with MSVC](https://github.com/cppalliance/http_proto/issues/214).
+
+- Mark **all public exception types** and **public classes used as the operand of `dynamic_cast`** with  
+  `BOOST_HTTP_PROTO_DECL`.
+
+  - This ensures:
+    - RTTI (typeinfo) is exported from DLLs.
+    - RTTI is visible from DSOs.
+  - Once a class is marked with `BOOST_HTTP_PROTO_DECL`, **all of its member functions are exported automatically**.
+    - Do **not** mark the member functions individually.
diff --git a/include/boost/http_proto/detail/config.hpp b/include/boost/http_proto/detail/config.hpp
index 2a3f0ad3..a60d4a55 100644
--- a/include/boost/http_proto/detail/config.hpp
+++ b/include/boost/http_proto/detail/config.hpp
@@ -33,6 +33,12 @@ namespace http_proto {
 #  define BOOST_HTTP_PROTO_DECL
 # endif
 
+#if defined(__MINGW32__)
+    #define BOOST_HTTP_PROTO_SYMBOL_VISIBLE BOOST_HTTP_PROTO_DECL
+#else
+    #define BOOST_HTTP_PROTO_SYMBOL_VISIBLE BOOST_SYMBOL_VISIBLE
+#endif
+
 # if !defined(BOOST_HTTP_PROTO_SOURCE) && !defined(BOOST_ALL_NO_LIB) && !defined(BOOST_HTTP_PROTO_NO_LIB)
 #  define BOOST_LIB_NAME boost_http_proto
 #  if defined(BOOST_ALL_DYN_LINK) || defined(BOOST_HTTP_PROTO_DYN_LINK)
diff --git a/include/boost/http_proto/impl/error.hpp b/include/boost/http_proto/impl/error.hpp
index 75e107d8..a04362bd 100644
--- a/include/boost/http_proto/impl/error.hpp
+++ b/include/boost/http_proto/impl/error.hpp
@@ -41,7 +41,7 @@ namespace http_proto {
 
 namespace detail {
 
-struct BOOST_SYMBOL_VISIBLE
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
     error_cat_type
     : system::error_category
 {
@@ -58,7 +58,7 @@ struct BOOST_SYMBOL_VISIBLE
     }
 };
 
-struct BOOST_SYMBOL_VISIBLE
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
     condition_cat_type
     : system::error_category
 {
diff --git a/include/boost/http_proto/server/route_handler.hpp b/include/boost/http_proto/server/route_handler.hpp
index 399310d5..2db4e40a 100644
--- a/include/boost/http_proto/server/route_handler.hpp
+++ b/include/boost/http_proto/server/route_handler.hpp
@@ -34,7 +34,7 @@ struct acceptor_config
 
 /** Parameters object for HTTP route handlers
 */
-struct BOOST_SYMBOL_VISIBLE
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
     route_params : route_params_base
 {
     /** The complete request target
@@ -180,7 +180,7 @@ post(F&& f) -> route_result
     if(task_)
         detail::throw_invalid_argument();
 
-    struct BOOST_SYMBOL_VISIBLE
+    struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
         immediate : detacher::owner
     {
         route_result rv;
@@ -193,7 +193,7 @@ post(F&& f) -> route_result
         }
     };
 
-    class BOOST_SYMBOL_VISIBLE model
+    class BOOST_HTTP_PROTO_SYMBOL_VISIBLE model
         : public task
         , public detacher::owner
     {
diff --git a/include/boost/http_proto/server/router_types.hpp b/include/boost/http_proto/server/router_types.hpp
index 39f2306f..0b16d9d4 100644
--- a/include/boost/http_proto/server/router_types.hpp
+++ b/include/boost/http_proto/server/router_types.hpp
@@ -36,7 +36,7 @@ using route_result = system::error_code;
 
     These values determine how the caller proceeds after invoking
     a route handler. Each enumerator represents a distinct control
-    action—whether the request was handled, should continue to the
+    action�whether the request was handled, should continue to the
     next route, transfers ownership of the session, or signals that
     the connection should be closed.
 */
@@ -111,7 +111,7 @@ struct is_error_code_enum<
 namespace http_proto {
 
 namespace detail {
-struct BOOST_SYMBOL_VISIBLE route_cat_type
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE route_cat_type
     : system::error_category
 {
     BOOST_HTTP_PROTO_DECL const char* name() const noexcept override;
@@ -162,7 +162,7 @@ class detacher
 public:
     /** Base class of the implementation
     */
-    struct BOOST_SYMBOL_VISIBLE
+    struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
         owner
     {
         BOOST_HTTP_PROTO_DECL virtual resumer do_detach();
diff --git a/include/boost/http_proto/sink.hpp b/include/boost/http_proto/sink.hpp
index 8445be7b..2e1ed88f 100644
--- a/include/boost/http_proto/sink.hpp
+++ b/include/boost/http_proto/sink.hpp
@@ -36,7 +36,7 @@ namespace http_proto {
         @ref source,
         @ref parser.
 */
-struct BOOST_HTTP_PROTO_DECL
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
     sink
 {
     /** The results of consuming data.
@@ -188,6 +188,7 @@ struct BOOST_HTTP_PROTO_DECL
         @param more `true` if there will be one
         or more subsequent calls.
     */
+    BOOST_HTTP_PROTO_DECL
     virtual
     results
     on_write(
diff --git a/include/boost/http_proto/source.hpp b/include/boost/http_proto/source.hpp
index 6be07b41..6e719f57 100644
--- a/include/boost/http_proto/source.hpp
+++ b/include/boost/http_proto/source.hpp
@@ -36,7 +36,7 @@ namespace http_proto {
         @ref sink,
         @ref serializer.
 */
-struct BOOST_HTTP_PROTO_DECL
+struct BOOST_HTTP_PROTO_SYMBOL_VISIBLE
     source
 {
     /** The results of producing data.
@@ -191,6 +191,7 @@ struct BOOST_HTTP_PROTO_DECL
         indicate failure or that no more
         data remains (or both).
     */
+    BOOST_HTTP_PROTO_DECL
     virtual
     results
     on_read(