diff --git a/include/ipmid/message/pack.hpp b/include/ipmid/message/pack.hpp
index 0075000..86a12be 100644
--- a/include/ipmid/message/pack.hpp
+++ b/include/ipmid/message/pack.hpp
@@ -131,7 +131,7 @@
 
 /** @brief Specialization of PackSingle for fixed_uint_t types
  */
-template <unsigned N>
+template <bitcount_t N>
 struct PackSingle<fixed_uint_t<N>>
 {
     static int op(Payload& p, const fixed_uint_t<N>& t)
diff --git a/include/ipmid/message/types.hpp b/include/ipmid/message/types.hpp
index 7a2168e..1da2574 100644
--- a/include/ipmid/message/types.hpp
+++ b/include/ipmid/message/types.hpp
@@ -17,17 +17,24 @@
 
 #include <bitset>
 #include <boost/multiprecision/cpp_int.hpp>
+#include <boost/version.hpp>
 #include <ipmid/utility.hpp>
 #include <tuple>
 
+#if BOOST_VERSION < 107900
+using bitcount_t = unsigned;
+#else
+using bitcount_t = std::size_t;
+#endif
+
 // unsigned fixed-bit sizes
-template <unsigned N>
+template <bitcount_t N>
 using fixed_uint_t =
     boost::multiprecision::number<boost::multiprecision::cpp_int_backend<
         N, N, boost::multiprecision::unsigned_magnitude,
         boost::multiprecision::unchecked, void>>;
 // signed fixed-bit sizes
-template <unsigned N>
+template <bitcount_t N>
 using fixed_int_t =
     boost::multiprecision::number<boost::multiprecision::cpp_int_backend<
         N, N, boost::multiprecision::signed_magnitude,
@@ -79,17 +86,17 @@
 namespace details
 {
 
-template <size_t N>
+template <bitcount_t N>
 struct Size
 {
-    static constexpr size_t value = N;
+    static constexpr bitcount_t value = N;
 };
 
-template <unsigned Bits>
+template <bitcount_t Bits>
 constexpr auto getNrBits(const fixed_int_t<Bits>&) -> Size<Bits>;
-template <unsigned Bits>
+template <bitcount_t Bits>
 constexpr auto getNrBits(const fixed_uint_t<Bits>&) -> Size<Bits>;
-template <size_t Bits>
+template <bitcount_t Bits>
 constexpr auto getNrBits(const std::bitset<Bits>&) -> Size<Bits>;
 
 template <typename U>
diff --git a/include/ipmid/message/unpack.hpp b/include/ipmid/message/unpack.hpp
index 4ac4916..3a80c3f 100644
--- a/include/ipmid/message/unpack.hpp
+++ b/include/ipmid/message/unpack.hpp
@@ -157,7 +157,7 @@
 
 /** @brief Specialization of UnpackSingle for fixed_uint_t types
  */
-template <unsigned N>
+template <bitcount_t N>
 struct UnpackSingle<fixed_uint_t<N>>
 {
     static int op(Payload& p, fixed_uint_t<N>& t)