diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index 4ea3793..2190e3b 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -1440,6 +1440,8 @@
   void AtomicPropertySetterGetterRules(ObjCImplDecl* IMPDecl,
                                        ObjCContainerDecl* IDecl);
 
+  void DiagnoseDuplicateIvars(ObjCInterfaceDecl *ID, ObjCInterfaceDecl *SID);
+
   /// MatchTwoMethodDeclarations - Checks if two methods' type match and returns
   /// true, or false, accordingly.
   bool MatchTwoMethodDeclarations(const ObjCMethodDecl *Method,
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 0be3841..27eb251 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -5659,21 +5659,8 @@
       }
       // Must enforce the rule that ivars in the base classes may not be
       // duplicates.
-      if (ID->getSuperClass()) {
-        for (ObjCInterfaceDecl::ivar_iterator IVI = ID->ivar_begin(),
-             IVE = ID->ivar_end(); IVI != IVE; ++IVI) {
-          ObjCIvarDecl* Ivar = (*IVI);
-
-          if (IdentifierInfo *II = Ivar->getIdentifier()) {
-            ObjCIvarDecl* prevIvar =
-              ID->getSuperClass()->lookupInstanceVariable(II);
-            if (prevIvar) {
-              Diag(Ivar->getLocation(), diag::err_duplicate_member) << II;
-              Diag(prevIvar->getLocation(), diag::note_previous_declaration);
-            }
-          }
-        }
-      }
+      if (ID->getSuperClass())
+        DiagnoseDuplicateIvars(ID, ID->getSuperClass());
     } else if (ObjCImplementationDecl *IMPDecl =
                   dyn_cast<ObjCImplementationDecl>(EnclosingDecl)) {
       assert(IMPDecl && "ActOnFields - missing ObjCImplementationDecl");
diff --git a/lib/Sema/SemaDeclObjC.cpp b/lib/Sema/SemaDeclObjC.cpp
index 925c0db..939ccab 100644
--- a/lib/Sema/SemaDeclObjC.cpp
+++ b/lib/Sema/SemaDeclObjC.cpp
@@ -1781,6 +1781,29 @@
   }
 }
 
+/// DiagnoseDuplicateIvars - 
+/// Check for duplicate ivars in the entire class at the start of 
+/// @implementation. This becomes necesssary because class extension can
+/// add ivars to a class in random order which will not be known until
+/// class's @implementation is seen.
+void Sema::DiagnoseDuplicateIvars(ObjCInterfaceDecl *ID, 
+                                  ObjCInterfaceDecl *SID) {
+  for (ObjCInterfaceDecl::ivar_iterator IVI = ID->ivar_begin(),
+       IVE = ID->ivar_end(); IVI != IVE; ++IVI) {
+    ObjCIvarDecl* Ivar = (*IVI);
+    if (Ivar->isInvalidDecl())
+      continue;
+    if (IdentifierInfo *II = Ivar->getIdentifier()) {
+      ObjCIvarDecl* prevIvar = SID->lookupInstanceVariable(II);
+      if (prevIvar) {
+        Diag(Ivar->getLocation(), diag::err_duplicate_member) << II;
+        Diag(prevIvar->getLocation(), diag::note_previous_declaration);
+        Ivar->setInvalidDecl();
+      }
+    }
+  }
+}
+
 // Note: For class/category implemenations, allMethods/allProperties is
 // always null.
 void Sema::ActOnAtEnd(SourceRange AtEnd,
@@ -1892,6 +1915,11 @@
     if (ObjCInterfaceDecl* IDecl = IC->getClassInterface()) {
       ImplMethodsVsClassMethods(IC, IDecl);
       AtomicPropertySetterGetterRules(IC, IDecl);
+      if (LangOpts.ObjCNonFragileABI2)
+        while (IDecl->getSuperClass()) {
+          DiagnoseDuplicateIvars(IDecl, IDecl->getSuperClass());
+          IDecl = IDecl->getSuperClass();
+        }
     }
   } else if (ObjCCategoryImplDecl* CatImplClass =
                                    dyn_cast<ObjCCategoryImplDecl>(ClassDecl)) {