diff --git a/include/boost/asio/ip/detail/socket_option.hpp b/include/boost/asio/ip/detail/socket_option.hpp
index fddf6b87..cf49bdd7 100644
--- a/include/boost/asio/ip/detail/socket_option.hpp
+++ b/include/boost/asio/ip/detail/socket_option.hpp
@@ -38,7 +38,7 @@ template <int IPv4_Level, int IPv4_Name, int IPv6_Level, int IPv6_Name>
 class boolean
 {
 public:
-#if defined(__sun)
+#if defined(__sun) || defined(_AIX)
   typedef unsigned char value_type;
 #else
   typedef int value_type;