diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index 533386cab5..25f2164ed0 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -887,7 +887,7 @@ public:
   NamespaceDecl *GetStdNamespace();
   
   bool isPropertyReadonly(ObjCPropertyDecl *PropertyDecl,
-                          ObjCInterfaceDecl *IDecl) const;
+                          ObjCInterfaceDecl *IDecl);
                            
   /// CheckProtocolMethodDefs - This routine checks unimplemented
   /// methods declared in protocol, and those referenced by it.
diff --git a/lib/Sema/SemaDeclObjC.cpp b/lib/Sema/SemaDeclObjC.cpp
index b3644a5ab9..cb35890b3f 100644
--- a/lib/Sema/SemaDeclObjC.cpp
+++ b/lib/Sema/SemaDeclObjC.cpp
@@ -720,7 +720,7 @@ void Sema::WarnConflictingTypedMethods(ObjCMethodDecl *ImpMethodDecl,
 /// for the property in the class and in its categories and implementations
 ///
 bool Sema::isPropertyReadonly(ObjCPropertyDecl *PDecl,
-                              ObjCInterfaceDecl *IDecl) const {
+                              ObjCInterfaceDecl *IDecl) {
   // by far the most common case.
   if (!PDecl->isReadOnly())
     return false;
@@ -758,6 +758,11 @@ bool Sema::isPropertyReadonly(ObjCPropertyDecl *PDecl,
         return false;
     }
   }
+  // Lastly, look through the implementation (if one is in scope).
+  if (ObjCImplementationDecl *ImpDecl = 
+        ObjCImplementations[IDecl->getIdentifier()])
+    if (ImpDecl->getInstanceMethod(PDecl->getSetterName()))
+      return false;
   return true;
 }
 
diff --git a/test/SemaObjC/property-13.m b/test/SemaObjC/property-13.m
new file mode 100644
index 0000000000..bcf8299a4f
--- /dev/null
+++ b/test/SemaObjC/property-13.m
@@ -0,0 +1,77 @@
+// RUN: clang -fsyntax-only -verify %s
+
+@interface NSObject 
++ alloc;
+- init;
+@end
+
+@protocol Test
+  @property int required;
+
+@optional
+  @property int optional;
+  @property int optional1;
+  @property int optional_preexisting_setter_getter;
+  @property (setter = setOptional_preexisting_setter_getter: ,
+	     getter = optional_preexisting_setter_getter) int optional_with_setter_getter_attr;
+@required
+  @property int required1;
+@optional
+  @property int optional_to_be_defined;
+  @property (readonly, getter = optional_preexisting_setter_getter) int optional_getter_attr;
+@end
+
+@interface Test : NSObject <Test> {
+  int ivar;
+  int ivar1;
+  int ivar2;
+}
+@property int required;
+@property int optional_to_be_defined;
+- (int) optional_preexisting_setter_getter;
+- (void) setOptional_preexisting_setter_getter:(int)value;
+@end
+
+@implementation Test
+@synthesize required = ivar;
+@synthesize required1 = ivar1;
+@synthesize optional_to_be_defined = ivar2;
+- (int) optional_preexisting_setter_getter { return ivar; }
+- (void) setOptional_preexisting_setter_getter:(int)value
+	   {
+		ivar = value;
+	   }
+- (void) setOptional_getter_attr:(int)value { ivar = value; }
+@end
+
+int main ()
+{
+	Test *x = [[Test alloc] init];
+	/* 1. Test of a requred property */
+	x.required1 = 100;
+  	if (x.required1 != 100)
+	  abort ();
+
+	/* 2. Test of a synthesize optional property */
+  	x.optional_to_be_defined = 123;
+	if (x.optional_to_be_defined != 123)
+	  abort ();
+
+	/* 3. Test of optional property with pre-sxisting defined setter/getter */
+	x.optional_preexisting_setter_getter = 200;
+	if (x.optional_preexisting_setter_getter != 200)
+	  abort ();
+
+	/* 4. Test of optional property with setter/getter attribute */
+	if (x.optional_with_setter_getter_attr != 200)
+	  abort ();
+	return 0;
+
+	/* 5. Test of optional property with getter attribute and default setter method. */
+	x.optional_getter_attr = 1000;
+        if (x.optional_getter_attr != 1000)
+	  abort ();
+
+	return 0;
+}
+