diff --git a/include/boost/predef/os/unix.h b/include/boost/predef/os/unix.h
index 3d1dcb0..1ba06c9 100644
--- a/include/boost/predef/os/unix.h
+++ b/include/boost/predef/os/unix.h
@@ -28,10 +28,8 @@ http://www.boost.org/LICENSE_1_0.txt)
 
 #define BOOST_OS_UNIX BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
-#if !defined(BOOST_PREDEF_DETAIL_OS_DETECTED) && ( \
-    defined(unix) || defined(__unix) || \
-    defined(_XOPEN_SOURCE) || defined(_POSIX_SOURCE) \
-    )
+#if defined(unix) || defined(__unix) || \
+    defined(_XOPEN_SOURCE) || defined(_POSIX_SOURCE)
 #   undef BOOST_OS_UNIX
 #   define BOOST_OS_UNIX BOOST_VERSION_NUMBER_AVAILABLE
 #endif