diff --git a/clang/Sema/SemaDecl.cpp b/clang/Sema/SemaDecl.cpp
index 42024b1adb4c..ca39e6e606bb 100644
--- a/clang/Sema/SemaDecl.cpp
+++ b/clang/Sema/SemaDecl.cpp
@@ -868,13 +868,30 @@ Sema::DeclTy *Sema::ObjcStartClassInterface(SourceLocation AtInterfaceLoc,
                     IdentifierInfo **ProtocolNames, unsigned NumProtocols,
                     AttributeList *AttrList) {
   assert(ClassName && "Missing class identifier");
-  ObjcInterfaceDecl *IDecl;
-    
+   
+  ObjcInterfaceDecl* IDecl;
+  
+  if (Context.getObjCInterfaceDecl(ClassName))
+    Diag(AtInterfaceLoc, diag::err_duplicate_class_def, ClassName->getName());
+  
   IDecl = new ObjcInterfaceDecl(AtInterfaceLoc, ClassName);
   
   // Chain & install the interface decl into the identifier.
   IDecl->setNext(ClassName->getFETokenInfo<ScopedDecl>());
   ClassName->setFETokenInfo(IDecl);
+  
+  if (SuperName) {
+    const ObjcInterfaceDecl* SuperClassEntry = 
+                               Context.getObjCInterfaceDecl(SuperName);
+                              
+    if (!SuperClassEntry) {
+      Diag(AtInterfaceLoc, diag::err_undef_superclass, SuperName->getName(),
+           ClassName->getName());  
+    }
+  }
+  
+  Context.setObjCInterfaceDecl(ClassName, IDecl);
+    
   return IDecl;
 }
 
diff --git a/clang/include/clang/AST/ASTContext.h b/clang/include/clang/AST/ASTContext.h
index 76a51fc254ae..f9a33e579507 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -37,8 +37,10 @@ class ASTContext {
   llvm::FoldingSet<FunctionTypeNoProto> FunctionTypeNoProtos;
   llvm::FoldingSet<FunctionTypeProto> FunctionTypeProtos;
   llvm::DenseMap<const RecordDecl*, const RecordLayout*> RecordLayoutInfo;
+  llvm::DenseMap<const IdentifierInfo*, const ObjcInterfaceDecl*> ClassNameInfo;
   RecordDecl *CFConstantStringTypeDecl;
 public:
+  
   SourceManager &SourceMgr;
   TargetInfo &Target;
   IdentifierTable &Idents;
@@ -157,6 +159,12 @@ public:
   /// position information.
   const RecordLayout &getRecordLayout(const RecordDecl *D, SourceLocation L);
   
+  const ObjcInterfaceDecl* getObjCInterfaceDecl(const IdentifierInfo* ClassName) 
+                             { return ClassNameInfo[ClassName]; }
+  void setObjCInterfaceDecl(const IdentifierInfo* ClassName,
+                            const ObjcInterfaceDecl* InterfaceDecl)
+  { ClassNameInfo[ClassName] = InterfaceDecl; }
+  
   //===--------------------------------------------------------------------===//
   //                            Type Operators
   //===--------------------------------------------------------------------===//
diff --git a/clang/include/clang/Basic/DiagnosticKinds.def b/clang/include/clang/Basic/DiagnosticKinds.def
index 059edecb868d..445f3bf2b80c 100644
--- a/clang/include/clang/Basic/DiagnosticKinds.def
+++ b/clang/include/clang/Basic/DiagnosticKinds.def
@@ -408,6 +408,11 @@ DIAG(err_objc_protocol_optional, ERROR,
      "@optional may be specified in protocols only")
 DIAG(err_missing_catch_finally, ERROR,
      "@try statment without a @catch and @finally clause")
+DIAG(err_undef_superclass, ERROR,
+     "cannot find interface declaration for '%0', superclass of '%1'")
+DIAG(err_duplicate_class_def, ERROR,
+     "duplicate interface declaration for class '%0'")
+
 
 //===----------------------------------------------------------------------===//
 // Semantic Analysis
diff --git a/clang/test/Sema/undef-superclass-1.m b/clang/test/Sema/undef-superclass-1.m
new file mode 100644
index 000000000000..0b5b7c10d0bd
--- /dev/null
+++ b/clang/test/Sema/undef-superclass-1.m
@@ -0,0 +1,18 @@
+@class SUPER, Y;
+
+@interface INTF :SUPER  // expected-error {{cannot find interface declaration for 'SUPER', superclass of 'INTF'}}
+@end
+
+@interface SUPER @end
+
+@interface INTF1 : SUPER
+@end
+
+@interface INTF2 : INTF1
+@end
+
+@interface INTF3 : Y // expected-error {{cannot find interface declaration for 'Y', superclass of 'INTF3'}}
+@end
+
+@interface INTF1  // expected-error {{duplicate interface declaration for class 'INTF1'}}
+@end