diff --git a/src/system.h b/src/system.h
index fdefc1e..dc21bba 100644
--- a/src/system.h
+++ b/src/system.h
@@ -45,11 +45,11 @@
 
 #if ! defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 700
 #  undef _XOPEN_SOURCE
-#  if ! defined(__sun__)
-#      define _XOPEN_SOURCE	700	// Use SUSv4 where possible
+#  if defined(__sun) && defined(__SVR4)
+#      define _XOPEN_SOURCE	600	// Use SUSv3 on SunOS 5.x
+#      define __EXTENSIONS__	1	// ... with Solaris extensions
 #  else
-#      define _XOPEN_SOURCE	600	// Except on SunOS 5.x
-#      define __EXTENSIONS__	1	// ... but use Solaris extensions
+#      define _XOPEN_SOURCE	700	// Use SUSv4 everywhere else
 #  endif
 #endif