diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a1b0097cb8d..1ab1c66f7ad 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2005-11-03  Andrew Pinski  <pinskia@physics.uc.edu>
+
+	PR middle-end/23155
+	* gimplifier.c (gimplify_expr): Create a temporary for lvalue
+	CONSTRUCTOR.
+
 2005-11-03  Daniel Berlin  <dberlin@dberlin.org>
 
 	Fix PR tree-optimization/24351
diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index 52e70bdad5e..9e25aef25c2 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -4323,6 +4323,15 @@ gimplify_expr (tree *expr_p, tree *pre_p, tree *post_p,
 	      *expr_p = temp;
 	      ret = GS_OK;
 	    }
+	  /* C99 code may assign to an array in a constructed
+	     structure or union, and this has undefined behavior only
+	     on execution, so create a temporary if an lvalue is
+	     required.  */
+	  else if (fallback == fb_lvalue)
+	    {
+	      *expr_p = get_initialized_tmp_var (*expr_p, pre_p, post_p);
+	      lang_hooks.mark_addressable (*expr_p);
+	    }
 	  else
 	    ret = GS_ALL_DONE;
 	  break;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ffb3ee09409..9678651670f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2005-11-03  Andrew Pinski  <pinskia@physics.uc.edu>
+
+	PR middle-end/23155 
+	* g++.dg/ext/c99struct1.C: New test.
+	* gcc.dg/union-cast-1.c: New test.
+	* gcc.dg/union-cast-2.c: New test.
+	* gcc.dg/union-cast-3.c: New test.
+
 2005-11-03  Andrew Pinski  <pinskia@physics.uc.edu>
 
 	PR middle-end/24589
diff --git a/gcc/testsuite/g++.dg/ext/c99struct1.C b/gcc/testsuite/g++.dg/ext/c99struct1.C
new file mode 100644
index 00000000000..93e84b46039
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/c99struct1.C
@@ -0,0 +1,12 @@
+// { dg-options "" }
+// C99 anon struct variable with array accesses.
+
+struct s { int a[1]; };
+
+void
+foo5 (void)
+{
+	  ((struct s) { { 0 } }).a[0] = 1;
+}
+
+
diff --git a/gcc/testsuite/gcc.dg/union-cast-1.c b/gcc/testsuite/gcc.dg/union-cast-1.c
new file mode 100644
index 00000000000..1d7f4d549d8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/union-cast-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-std=gnu89" } */
+/* A combine of two extensions to C89 are used here.
+   First casts to unions is used.
+   Second subscripting non lvalue arrays, this is in C99. */
+
+union vx {short f[8]; int v;};
+int vec;
+
+void
+foo5 (int vec)
+{
+  ((union vx) vec).f[5] = 1;
+}
diff --git a/gcc/testsuite/gcc.dg/union-cast-2.c b/gcc/testsuite/gcc.dg/union-cast-2.c
new file mode 100644
index 00000000000..9aac5caa291
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/union-cast-2.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c89 -pedantic-errors" } */
+/* PR 23155
+   We should get two error messages, one about union cast
+   and the other about array access for non lvalues.  */
+
+
+union vx {short f[8]; int v;};
+int vec;
+
+void
+foo5 (int vec)
+{
+  ((union vx) vec).f[5] = 1; /* { dg-error "(forbids subscripting)|(forbids casts to union type)" } */
+}
diff --git a/gcc/testsuite/gcc.dg/union-cast-3.c b/gcc/testsuite/gcc.dg/union-cast-3.c
new file mode 100644
index 00000000000..5f9b9f86870
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/union-cast-3.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c99 -pedantic-errors" } */
+/* PR 23155
+   We should get one error messag, one about union cast. */
+
+
+union vx {short f[8]; int v;};
+int vec;
+
+void
+foo5 (int vec)
+{
+  ((union vx) vec).f[5] = 1; /* { dg-error "forbids casts to union type" } */
+}