diff --git a/Jamfile b/Jamfile
index 38c82d7d9..ea2bce8c9 100755
--- a/Jamfile
+++ b/Jamfile
@@ -264,7 +264,7 @@ rule building ( properties * )
 		# in shared object interfaces, so when it's
 		# enabled, just export everything (since we're)
 		# probably not a production build anyway
-		&& !<debug-iterators>on in $(properties)
+		&& ! <debug-iterators>on in $(properties)
 	{
 		# hide non-external symbols
 		# use ms-compat because boost.asio (as of 1.47.0
diff --git a/src/asio.cpp b/src/asio.cpp
index 0688e3f2b..52cc3c48c 100644
--- a/src/asio.cpp
+++ b/src/asio.cpp
@@ -79,6 +79,16 @@
 
 #else // _MSC_VER
 
+#include "libtorrent/config.hpp"
+
+#define TORRENT_HAS_ASIO_DECL x ## BOOST_ASIO_DECL
+
+// only define BOOST_ASIO_DECL if it hasn't already been defined
+// or if it has been defined to an empty string
+#if TORRENT_HAS_ASIO_DECL == x
+#define BOOST_ASIO_DECL BOOST_SYMBOL_EXPORT
+#endif
+
 #if BOOST_VERSION >= 104500
 #include <boost/asio/impl/src.hpp>
 #elif BOOST_VERSION >= 104400