diff --git a/include/boost/math/special_functions/detail/unchecked_factorial.hpp b/include/boost/math/special_functions/detail/unchecked_factorial.hpp
index 3bdc45fe5f..5fa9f0b6b4 100644
--- a/include/boost/math/special_functions/detail/unchecked_factorial.hpp
+++ b/include/boost/math/special_functions/detail/unchecked_factorial.hpp
@@ -1009,7 +1009,7 @@ struct max_factorial
 
 #ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION
 template <class T>
-const unsigned max_factorial<T>::value;
+constexpr unsigned max_factorial<T>::value;
 #endif
 
 } // namespace math