diff --git a/include/boost/functional/hash/detail/float_functions.hpp b/include/boost/functional/hash/detail/float_functions.hpp
index f766ec9..01cac09 100644
--- a/include/boost/functional/hash/detail/float_functions.hpp
+++ b/include/boost/functional/hash/detail/float_functions.hpp
@@ -96,6 +96,11 @@ namespace BOOST_HASH_DETECT_FLOAT_FUNCTIONS {
 // Then the call_* functions select an appropriate implementation.
 //
 // I used c99_func in a few places just to get a unique name.
+//
+// Important: when using 'using namespace' at namespace level, include as
+// little as possible in that namespace, as Visual C++ has an odd bug which
+// can cause the namespace to be imported at the global level. This seems to
+// happen mainly when there's a template in the same namesapce.
 
 #define BOOST_HASH_CALL_FLOAT_FUNC(cpp_func, c99_func, type1, type2)    \
 namespace BOOST_HASH_DETECT_FLOAT_FUNCTIONS {                           \