diff --git a/include/boost/config/compiler/clang.hpp b/include/boost/config/compiler/clang.hpp
index 90f747c0..1ecd85e3 100644
--- a/include/boost/config/compiler/clang.hpp
+++ b/include/boost/config/compiler/clang.hpp
@@ -261,7 +261,7 @@
 #endif
 
 // Clang has supported the 'unused' attribute since the first release.
-#define BOOST_ATTRIBUTE_UNUSED __attribute__((unused))
+#define BOOST_ATTRIBUTE_UNUSED __attribute__((__unused__))
 
 #ifndef BOOST_COMPILER
 #  define BOOST_COMPILER "Clang version " __clang_version__
diff --git a/include/boost/config/compiler/gcc.hpp b/include/boost/config/compiler/gcc.hpp
index 07147ee0..350431d0 100644
--- a/include/boost/config/compiler/gcc.hpp
+++ b/include/boost/config/compiler/gcc.hpp
@@ -276,7 +276,7 @@
 //
 // Unused attribute:
 #if __GNUC__ >= 4
-#  define BOOST_ATTRIBUTE_UNUSED __attribute__((unused))
+#  define BOOST_ATTRIBUTE_UNUSED __attribute__((__unused__))
 #endif
 
 #ifndef BOOST_COMPILER