Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -367,6 +367,7 @@
 def BadFunctionCast : DiagGroup<"bad-function-cast">;
 def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
 def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
+def ObjCPropertyAssignOnObjectType : DiagGroup<"objc-property-assign-on-object-type">;
 def ObjCProtocolQualifiers : DiagGroup<"objc-protocol-qualifiers">;
 def ObjCMissingSuperCalls : DiagGroup<"objc-missing-super-calls">;
 def ObjCDesignatedInit : DiagGroup<"objc-designated-initializers">;
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -1014,6 +1014,9 @@
   "property attributes '%0' and '%1' are mutually exclusive">;
 def err_objc_property_requires_object : Error<
   "property with '%0' attribute must be of object type">;
+def warn_objc_property_assign_on_object : Warning<
+  "'assign' property of object type may become a dangling reference; consider using 'unsafe_unretained'">,
+  InGroup<ObjCPropertyAssignOnObjectType>, DefaultIgnore;
 def warn_objc_property_no_assignment_attribute : Warning<
   "no 'assign', 'retain', or 'copy' attribute is specified - "
   "'assign' is assumed">,
Index: lib/Sema/SemaObjCProperty.cpp
===================================================================
--- lib/Sema/SemaObjCProperty.cpp
+++ lib/Sema/SemaObjCProperty.cpp
@@ -2547,6 +2547,14 @@
     PropertyDecl->setInvalidDecl();
   }
 
+  // Check for assign on object types.
+  if ((Attributes & ObjCDeclSpec::DQ_PR_assign) &&
+      !(Attributes & ObjCDeclSpec::DQ_PR_unsafe_unretained) &&
+      PropertyTy->isObjCRetainableType() &&
+      !PropertyTy->isObjCARCImplicitlyUnretainedType()) {
+    Diag(Loc, diag::warn_objc_property_assign_on_object);
+  }
+
   // Check for more than one of { assign, copy, retain }.
   if (Attributes & ObjCDeclSpec::DQ_PR_assign) {
     if (Attributes & ObjCDeclSpec::DQ_PR_copy) {
Index: test/SemaObjC/property-assign-on-object-type.m
===================================================================
--- /dev/null
+++ test/SemaObjC/property-assign-on-object-type.m
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wobjc-property-assign-on-object-type %s
+
+@interface Foo @end
+@protocol Prot @end
+
+@interface Bar
+@property(assign, readonly) Foo* o1; // expected-warning {{'assign' property of object type may become a dangling reference; consider using 'unsafe_unretained'}}
+@property(unsafe_unretained, readonly) Foo* o2;
+
+@property(assign) Class classProperty;
+@property(assign) Class<Prot> classWithProtocolProperty;
+@property(assign) int s1;
+@property(assign) int* s2;
+@end
+
+@interface Bar ()
+@property(readwrite) Foo* o1;
+@property(readwrite) Foo* o2;
+@end
Index: test/SemaObjC/property-in-class-extension-1.m
===================================================================
--- test/SemaObjC/property-in-class-extension-1.m
+++ test/SemaObjC/property-in-class-extension-1.m
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1  -fsyntax-only -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak -fobjc-weak -verify -Weverything %s
-// RUN: %clang_cc1 -x objective-c++ -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak -fobjc-weak -fsyntax-only -verify -Weverything %s
+// RUN: %clang_cc1  -fsyntax-only -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak -fobjc-weak -verify -Wproperty-attribute-mismatch %s
+// RUN: %clang_cc1 -x objective-c++ -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak -fobjc-weak -fsyntax-only -verify -Wproperty-attribute-mismatch %s
 // rdar://12103400
 
 @class NSString;