diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index a9b5f36..4cb7712 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -552,6 +552,8 @@
     return "BaseToDerived";
   case CastExpr::CK_DerivedToBase:
     return "DerivedToBase";
+  case CastExpr::CK_UncheckedDerivedToBase:
+    return "UncheckedDerivedToBase";
   case CastExpr::CK_Dynamic:
     return "Dynamic";
   case CastExpr::CK_ToUnion:
diff --git a/lib/Checker/GRExprEngine.cpp b/lib/Checker/GRExprEngine.cpp
index 1afe091..04f8cc6 100644
--- a/lib/Checker/GRExprEngine.cpp
+++ b/lib/Checker/GRExprEngine.cpp
@@ -2306,6 +2306,7 @@
   case CastExpr::CK_AnyPointerToObjCPointerCast:
   case CastExpr::CK_AnyPointerToBlockPointerCast:
   case CastExpr::CK_DerivedToBase:
+  case CastExpr::CK_UncheckedDerivedToBase:
     // Delegate to SValuator to process.
     for (ExplodedNodeSet::iterator I = S2.begin(), E = S2.end(); I != E; ++I) {
       ExplodedNode* N = *I;
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 2ddc08a..027264f 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -1637,6 +1637,7 @@
   case CastExpr::CK_AnyPointerToObjCPointerCast:
     return EmitLValue(E->getSubExpr());
   
+  case CastExpr::CK_UncheckedDerivedToBase:
   case CastExpr::CK_DerivedToBase: {
     const RecordType *DerivedClassTy = 
       E->getSubExpr()->getType()->getAs<RecordType>();
diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index 1ef06cc..42bf68e 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -769,6 +769,9 @@
 
 static bool ShouldNullCheckClassCastValue(const CastExpr *CE) {
   const Expr *E = CE->getSubExpr();
+
+  if (CE->getCastKind() == CastExpr::CK_UncheckedDerivedToBase)
+    return false;
   
   if (isa<CXXThisExpr>(E)) {
     // We always assume that 'this' is never null.
@@ -826,6 +829,7 @@
     return CGF.GetAddressOfDerivedClass(Src, BaseClassDecl, DerivedClassDecl, 
                                         NullCheckValue);
   }
+  case CastExpr::CK_UncheckedDerivedToBase:
   case CastExpr::CK_DerivedToBase: {
     const RecordType *DerivedClassTy = 
       E->getType()->getAs<PointerType>()->getPointeeType()->getAs<RecordType>();
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index e232230..0980710 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -1461,7 +1461,7 @@
 
       if (PointerConversions)
         QType = Context.getPointerType(QType);
-      ImpCastExprToType(From, QType, CastExpr::CK_DerivedToBase,
+      ImpCastExprToType(From, QType, CastExpr::CK_UncheckedDerivedToBase,
                         /*isLvalue*/ !PointerConversions);
 
       FromType = QType;
@@ -1497,7 +1497,7 @@
       QualType UType = URecordType;
       if (PointerConversions)
         UType = Context.getPointerType(UType);
-      ImpCastExprToType(From, UType, CastExpr::CK_DerivedToBase,
+      ImpCastExprToType(From, UType, CastExpr::CK_UncheckedDerivedToBase,
                         /*isLvalue*/ !PointerConversions);
       FromType = UType;
       FromRecordType = URecordType;
@@ -1517,8 +1517,8 @@
 
   // FIXME: isLvalue should be !PointerConversions here, but codegen
   // does very silly things.
-  ImpCastExprToType(From, DestType, CastExpr::CK_DerivedToBase,
-                    /*isLvalue=*/ true);
+  ImpCastExprToType(From, DestType, CastExpr::CK_UncheckedDerivedToBase,
+                    /*isLvalue=*/ !PointerConversions);
   return false;
 }