--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/pr79983.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,15 @@
+/* PR c/79983 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+struct S;
+struct S { int i; }; /* { dg-message "originally defined here" } */
+struct S { int i, j; }; /* { dg-error "redefinition of 'struct S'" } */
+
+enum E;
+enum E { A, B, C }; /* { dg-message "originally defined here" } */
+enum E { D, F }; /* { dg-error "nested redefinition of 'enum E'|redeclaration of 'enum E'" } */
+
+union U;
+union U { int i; }; /* { dg-message "originally defined here" } */
+union U { int i; double d; }; /* { dg-error "redefinition of 'union U'" } */