--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/cpp/defined-syshdr.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,27 @@
+# 1 "defined-syshdr.c" 1
+/* { dg-do preprocess } */
+/* { dg-options "-Wexpansion-to-defined" } */
+
+#define defined_outside_sys_hdr   defined FOO
+
+# 36 "some-system-header.h" 1 3
+
+#define defined_inside_sys_hdr    defined FOO
+
+/* In a system header, it's acceptable.  */
+#if defined_outside_sys_hdr   /* { dg-bogus "may not be portable" } */
+#endif
+
+# 16 "defined-syshdr.c" 2
+
+/* Back to _not_ in a system header */
+
+#if defined_outside_sys_hdr   /* { dg-message "may not be portable" } */
+#endif
+
+/* Currently we warn about this, but it is probably a good idea not to.  */
+
+#if defined_inside_sys_hdr   /* { dg-bogus "may not be portable" "" { xfail *-*-* } } */
+#endif
+
+int x;