diff --git a/include/boost/math/tools/mp.hpp b/include/boost/math/tools/mp.hpp
index 7bf70a55a..55aac1b09 100644
--- a/include/boost/math/tools/mp.hpp
+++ b/include/boost/math/tools/mp.hpp
@@ -388,7 +388,7 @@ struct append_integer_sequence {};
 template<typename T, T... Index, T... J>
 struct append_integer_sequence<integer_sequence<T, Index...>, integer_sequence<T, J...>>
 {
-    using type = integer_sequence<T, Index..., (J + sizeof...(I))...>;
+    using type = integer_sequence<T, Index..., (J + sizeof...(Index))...>;
 };
 
 template<typename T, T N>