diff --git a/src/lib/libast/features/common b/src/lib/libast/features/common
index a01fcbeb4..fd6ff158a 100644
--- a/src/lib/libast/features/common
+++ b/src/lib/libast/features/common
@@ -36,12 +36,6 @@ cat{
 	#	define	__OPTIMIZE_SIZE__	1
 	#endif
 
-	/* enable POSIX standard on Solaris */
-	#ifdef __sun
-	#	undef	_XPG6
-	#	define	_XPG6		1
-	#endif
-
 	/* __STD_C indicates that the language is ANSI C or C++ */
 	#if !defined(__STD_C) && __STDC__
 	#	define	__STD_C		1
diff --git a/src/lib/libast/features/standards b/src/lib/libast/features/standards
index 5b6dcbb0e..75702d092 100644
--- a/src/lib/libast/features/standards
+++ b/src/lib/libast/features/standards
@@ -19,6 +19,18 @@ if tst note{ FreeBSD or DragonFly BSD }end compile{
 		#endif
 	}end {
 	}
+elif tst note{ SunOS (Solaris, illumos) }end compile{
+		#if !__sun
+		#error dark
+		#endif
+	}end {
+		#define _XPG7		1
+		#define	_XPG6		1
+		#define	_XPG5		1
+		#define _XPG4		1
+		#define	__EXTENSIONS__	1
+		#define	_XOPEN_SOURCE	9900
+	}
 elif tst note{ _ALL_SOURCE & _POSIX_SOURCE & _POSIX_C_SOURCE & _XOPEN_SOURCE & _GNU_SOURCE & _DARWIN_C_SOURCE & __EXTENSIONS__ works }end compile{
 		#define _ALL_SOURCE	1
 		#define _POSIX_SOURCE	1