diff --git a/doc/intrusive.qbk b/doc/intrusive.qbk
index 888c25b..5589df1 100644
--- a/doc/intrusive.qbk
+++ b/doc/intrusive.qbk
@@ -3886,6 +3886,14 @@ to be inserted in intrusive containers are allocated using `std::vector` or `std
 
 [section:release_notes Release Notes]
 
+[section:release_notes_boost_1_75_00 Boost 1.75 Release]
+
+*  Fixed bugs:
+   *  [@https://github.com/boostorg/intrusive/issues/52  GitHub #52: ['Invalid casting in BOOST_INTRUSIVE_BSR_INTRINSIC]]
+
+[endsect]
+
+
 [section:release_notes_boost_1_73_00 Boost 1.73 Release]
 
 *  Fixed bugs:
diff --git a/include/boost/intrusive/detail/math.hpp b/include/boost/intrusive/detail/math.hpp
index 0748f1d..c13e745 100644
--- a/include/boost/intrusive/detail/math.hpp
+++ b/include/boost/intrusive/detail/math.hpp
@@ -76,8 +76,8 @@ namespace detail {
    inline std::size_t floor_log2 (std::size_t x)
    {
       unsigned long log2;
-      BOOST_INTRUSIVE_BSR_INTRINSIC( &log2, (unsigned long)x );
-      return log2;
+      BOOST_INTRUSIVE_BSR_INTRINSIC( &log2, x );
+      return static_cast<std::size_t>(log2);
    }
 
    #undef BOOST_INTRUSIVE_BSR_INTRINSIC