diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -589,19 +589,21 @@
 bool ConstStructBuilder::AppendBitField(
     const FieldDecl *Field, uint64_t FieldOffset, llvm::ConstantInt *CI,
     bool AllowOverwrite) {
-  uint64_t FieldSize = Field->getBitWidthValue(CGM.getContext());
+  const CGRecordLayout &RL =
+      CGM.getTypes().getCGRecordLayout(Field->getParent());
+  const CGBitFieldInfo &Info = RL.getBitFieldInfo(Field);
   llvm::APInt FieldValue = CI->getValue();
 
   // Promote the size of FieldValue if necessary
   // FIXME: This should never occur, but currently it can because initializer
   // constants are cast to bool, and because clang is not enforcing bitfield
   // width limits.
-  if (FieldSize > FieldValue.getBitWidth())
-    FieldValue = FieldValue.zext(FieldSize);
+  if (Info.Size > FieldValue.getBitWidth())
+    FieldValue = FieldValue.zext(Info.Size);
 
   // Truncate the size of FieldValue to the bit field size.
-  if (FieldSize < FieldValue.getBitWidth())
-    FieldValue = FieldValue.trunc(FieldSize);
+  if (Info.Size < FieldValue.getBitWidth())
+    FieldValue = FieldValue.trunc(Info.Size);
 
   return Builder.addBits(FieldValue,
                          CGM.getContext().toBits(StartOffset) + FieldOffset,
diff --git a/clang/test/CodeGenCXX/bitfield-layout.cpp b/clang/test/CodeGenCXX/bitfield-layout.cpp
--- a/clang/test/CodeGenCXX/bitfield-layout.cpp
+++ b/clang/test/CodeGenCXX/bitfield-layout.cpp
@@ -1,11 +1,14 @@
-// RUN: %clang_cc1 %s -triple=x86_64-apple-darwin10 -emit-llvm -o - -O3 | FileCheck -check-prefix CHECK-LP64 %s
-// RUN: %clang_cc1 %s -triple=i386-apple-darwin10 -emit-llvm -o - -O3 | FileCheck -check-prefix CHECK-LP32 %s
+// RUN: %clang_cc1 %s -triple=x86_64-apple-darwin10 -emit-llvm -o - -O3 | FileCheck -check-prefix=CHECK-LP64 -check-prefix=CHECK %s
+// RUN: %clang_cc1 %s -triple=i386-apple-darwin10 -emit-llvm -o - -O3 | FileCheck -check-prefix CHECK-LP32 -check-prefix=CHECK %s
+// RUN: %clang_cc1 %s -triple=aarch64_be-none-eabi -emit-llvm -o - -O3 | FileCheck -check-prefix CHECK-A64BE -check-prefix=CHECK %s
+// RUN: %clang_cc1 %s -triple=thumbv7_be-none-eabi -emit-llvm -o - -O3 | FileCheck -check-prefix CHECK-A32BE -check-prefix=CHECK %s
 
 // CHECK-LP64: %union.Test1 = type { i32, [4 x i8] }
 union Test1 {
   int a;
   int b: 39;
-} t1;
+};
+Test1 t1;
 
 // CHECK-LP64: %union.Test2 = type { i8 }
 union Test2 {
@@ -17,10 +20,16 @@
   int : 9;
 } t3;
 
+// CHECK: %union.Test4 = type { i8, i8 }
+union Test4 {
+  char val : 16;
+};
+Test4 t4;
 
 #define CHECK(x) if (!(x)) return __LINE__
 
-int f() {
+// CHECK: define i32 @_Z11test_assignv()
+int test_assign() {
   struct {
     int a;
 
@@ -37,7 +46,41 @@
   CHECK(c.b == (unsigned long long)-1);
   CHECK(c.c == 0);
 
-// CHECK-LP64: ret i32 0
-// CHECK-LP32: ret i32 0
+  Test1 u1;
+  Test4 u2;
+
+  u1.b = 1;
+  u2.val = 42;
+
+  CHECK(u1.b == 1);
+  CHECK(u2.val == 42);
+
+  // CHECK: ret i32 0
+  return 0;
+}
+
+// CHECK: define i32 @_Z9test_initv()
+int test_init() {
+  struct S {
+    int a;
+
+    unsigned long long b : 65;
+
+    int c;
+  };
+  S s1 = {1, 42, 0};
+
+  CHECK(s1.a == 1);
+  CHECK(s1.b == (unsigned long long)42);
+  CHECK(s1.c == 0);
+
+  Test1 u1 = {1};
+  Test4 u2 = {42};
+
+  CHECK(u1.a == 1);
+  CHECK(u1.b == 1);
+  CHECK(u2.val == 42);
+
+  // CHECK: ret i32 0
   return 0;
 }