diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index 68e25e7..f0dd687 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -88,6 +88,19 @@
     << call->getArg(1)->getSourceRange();
 }
 
+/// CheckBuiltinAnnotationString - Checks that string argument to the builtin
+/// annotation is a non wide string literal.
+static bool CheckBuiltinAnnotationString(Sema &S, Expr *Arg) {
+  Arg = Arg->IgnoreParenCasts();
+  StringLiteral *Literal = dyn_cast<StringLiteral>(Arg);
+  if (!Literal || !Literal->isAscii()) {
+    S.Diag(Arg->getLocStart(), diag::err_builtin_annotation_not_string_constant)
+      << Arg->getSourceRange();
+    return true;
+  }
+  return false;
+}
+
 ExprResult
 Sema::CheckBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
   ExprResult TheCallResult(Owned(TheCall));
@@ -184,6 +197,10 @@
   case Builtin::BI__sync_lock_release:
   case Builtin::BI__sync_swap:
     return SemaBuiltinAtomicOverloaded(move(TheCallResult));
+  case Builtin::BI__builtin_annotation:
+    if (CheckBuiltinAnnotationString(*this, TheCall->getArg(1)))
+      return ExprError();
+    break;
   }
   
   // Since the target specific builtins for each arch overlap, only check those
@@ -640,7 +657,6 @@
   return move(TheCallResult);
 }
 
-
 /// CheckObjCString - Checks that the argument to the builtin
 /// CFString constructor is correct
 /// Note: It might also make sense to do the UTF-16 conversion here (would
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 355378e..d6137e5 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1461,8 +1461,14 @@
 static bool
 DeclHasAttr(const Decl *D, const Attr *A) {
   const OwnershipAttr *OA = dyn_cast<OwnershipAttr>(A);
+  const AnnotateAttr *Ann = dyn_cast<AnnotateAttr>(A);
   for (Decl::attr_iterator i = D->attr_begin(), e = D->attr_end(); i != e; ++i)
     if ((*i)->getKind() == A->getKind()) {
+      if (Ann) {
+        if (Ann->getAnnotation() == cast<AnnotateAttr>(*i)->getAnnotation())
+          return true;
+        continue;
+      }
       // FIXME: Don't hardcode this check
       if (OA && isa<OwnershipAttr>(*i))
         return OA->getOwnKind() == cast<OwnershipAttr>(*i)->getOwnKind();
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 624ac08..2f2e280 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -2484,6 +2484,14 @@
     S.Diag(ArgExpr->getLocStart(), diag::err_attribute_not_string) <<"annotate";
     return;
   }
+
+  // Don't duplicate annotations that are already set.
+  for (specific_attr_iterator<AnnotateAttr>
+       i = D->specific_attr_begin<AnnotateAttr>(),
+       e = D->specific_attr_end<AnnotateAttr>(); i != e; ++i) {
+      if ((*i)->getAnnotation() == SE->getString())
+          return;
+  }
   D->addAttr(::new (S.Context) AnnotateAttr(Attr.getLoc(), S.Context,
                                             SE->getString()));
 }