diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b4b7fe0b27e..66ca10b96b9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2018-08-21  Tamar Christina  <tamar.christina@arm.com>
+
+	* expmed.c (extract_low_bits): Reject invalid subregs early.
+
 2018-08-21  Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
 	PR middle-end/86121
diff --git a/gcc/expmed.c b/gcc/expmed.c
index be9f0ec9011..e2819309e4b 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -2392,6 +2392,10 @@ extract_low_bits (machine_mode mode, machine_mode src_mode, rtx src)
     return NULL_RTX;
 
   src = gen_lowpart (src_int_mode, src);
+  if (!validate_subreg (int_mode, src_int_mode, src,
+			subreg_lowpart_offset (int_mode, src_int_mode)))
+    return NULL_RTX;
+
   src = convert_modes (int_mode, src_int_mode, src, true);
   src = gen_lowpart (mode, src);
   return src;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ccdaa1e32a1..42117a60523 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-08-21  Tamar Christina  <tamar.christina@arm.com>
+
+	* gcc.target/aarch64/large_struct_copy.c: New test.
+
 2018-08-21  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	* g++.dg/torture/pr86763.C: Restrict to *-*-linux*.
diff --git a/gcc/testsuite/gcc.target/aarch64/large_struct_copy.c b/gcc/testsuite/gcc.target/aarch64/large_struct_copy.c
new file mode 100644
index 00000000000..2b5e7801bad
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/large_struct_copy.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef unsigned __attribute__((mode(DI))) uint64_t;
+
+struct S0 {
+  uint64_t f1;
+  uint64_t f2;
+  uint64_t f3;
+  uint64_t f4;
+  uint64_t f5;
+} a;
+struct S2 {
+  uint64_t f0;
+  uint64_t f2;
+  struct S0 f3;
+};
+
+void fn1 () {
+  struct S2 b = {0, 1, 7, 4073709551611, 4, 8, 7};
+  a = b.f3;
+}
+