diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 6f430ff..85ca9e9 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1669,6 +1669,15 @@
   "size of bit-field %0 (%1 bits) exceeds size of its type (%2 bits)">;
 def err_anon_bitfield_width_exceeds_type_size : Error<
   "size of anonymous bit-field (%0 bits) exceeds size of its type (%1 bits)">;
+  
+// Used by C++ which allows bit-fields that are wider than the type.
+def warn_bitfield_width_exceeds_type_size: Warning<
+  "size of bit-field %0 (%1 bits) exceeds the size of its type; value will be "
+  "truncated to %2 bits">;
+def warn_anon_bitfield_width_exceeds_type_size : Warning<
+  "size of anonymous bit-field (%0 bits) exceeds size of its type; value will "
+  "be truncated to %1 bits">;
+
 def warn_missing_braces : Warning<
   "suggest braces around initialization of subobject">,
   InGroup<DiagGroup<"missing-braces">>, DefaultIgnore;
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 2e8deac..182a85a 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -5375,11 +5375,23 @@
   if (!FieldTy->isDependentType()) {
     uint64_t TypeSize = Context.getTypeSize(FieldTy);
     if (Value.getZExtValue() > TypeSize) {
+      if (!getLangOptions().CPlusPlus) {
+        if (FieldName) 
+          return Diag(FieldLoc, diag::err_bitfield_width_exceeds_type_size)
+            << FieldName << (unsigned)Value.getZExtValue() 
+            << (unsigned)TypeSize;
+        
+        return Diag(FieldLoc, diag::err_anon_bitfield_width_exceeds_type_size)
+          << (unsigned)Value.getZExtValue() << (unsigned)TypeSize;
+      }
+      
       if (FieldName)
-        return Diag(FieldLoc, diag::err_bitfield_width_exceeds_type_size)
-          << FieldName << (unsigned)Value.getZExtValue() << (unsigned)TypeSize;
-      return Diag(FieldLoc, diag::err_anon_bitfield_width_exceeds_type_size)
-        << (unsigned)Value.getZExtValue() << (unsigned)TypeSize;
+        Diag(FieldLoc, diag::warn_bitfield_width_exceeds_type_size)
+          << FieldName << (unsigned)Value.getZExtValue() 
+          << (unsigned)TypeSize;
+      else
+        Diag(FieldLoc, diag::warn_anon_bitfield_width_exceeds_type_size)
+          << (unsigned)Value.getZExtValue() << (unsigned)TypeSize;        
     }
   }
 
diff --git a/test/SemaCXX/bitfield-layout.cpp b/test/SemaCXX/bitfield-layout.cpp
new file mode 100644
index 0000000..318a57f
--- /dev/null
+++ b/test/SemaCXX/bitfield-layout.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify -triple=x86_64-apple-darwin10
+
+#define CHECK_SIZE(name, size) extern int name##1[sizeof(name) == size ? 1 : -1];
+#define CHECK_ALIGN(name, size) extern int name##2[__alignof(name) == size ? 1 : -1];
+
+// Simple test.
+struct Test1 {
+  char c : 9; // expected-warning {{size of bit-field 'c' (9 bits) exceeds the size of its type; value will be truncated to 8 bits}}
+};
+CHECK_SIZE(Test1, 2);
+CHECK_ALIGN(Test1, 1);
+