diff --git a/doc/changes.qbk b/doc/changes.qbk
index 4e0d0a9..bc6f4ca 100644
--- a/doc/changes.qbk
+++ b/doc/changes.qbk
@@ -106,4 +106,12 @@
   Avoid hashing 0.5 and 0 to the same number.
 * Stop using deprecated `BOOST_HAS_*` macros.
 
+[h2 Boost 1.44.0]
+
+* Prevent implicit conversions when calling `hash_value`. If you find
+  that the new version breaks your code, you can enable the old
+  behaviour by defining `BOOST_HASH_ALLOW_IMPLICIT_CASTS` - although
+  I would recommend that you update your code to work with the new
+  version.
+
 [endsect]
diff --git a/include/boost/functional/hash/hash.hpp b/include/boost/functional/hash/hash.hpp
index bd8d37f..54407d6 100644
--- a/include/boost/functional/hash/hash.hpp
+++ b/include/boost/functional/hash/hash.hpp
@@ -30,6 +30,8 @@
 
 namespace boost
 {
+#if !defined(BOOST_HASH_ALLOW_IMPLICIT_CASTS)
+
     // If you get a static assertion here, it's because hash_value
     // isn't declared for your type.
     template <typename T>
@@ -38,6 +40,8 @@ namespace boost
         return 0;
     }
 
+#endif
+
     std::size_t hash_value(bool);
     std::size_t hash_value(char);
     std::size_t hash_value(unsigned char);