diff --git a/lib/Sema/SemaObjCProperty.cpp b/lib/Sema/SemaObjCProperty.cpp
index f9c064d..5df214f 100644
--- a/lib/Sema/SemaObjCProperty.cpp
+++ b/lib/Sema/SemaObjCProperty.cpp
@@ -1777,6 +1777,7 @@
           Attributes & ObjCDeclSpec::DQ_PR_copy ? "copy" : "retain (or strong)");
     Attributes &= ~(ObjCDeclSpec::DQ_PR_weak   | ObjCDeclSpec::DQ_PR_copy |
                     ObjCDeclSpec::DQ_PR_retain | ObjCDeclSpec::DQ_PR_strong);
+    PropertyDecl->setInvalidDecl();
   }
 
   // Check for more than one of { assign, copy, retain }.
diff --git a/test/SemaObjC/arc-property.m b/test/SemaObjC/arc-property.m
index 2993118..226b03b 100644
--- a/test/SemaObjC/arc-property.m
+++ b/test/SemaObjC/arc-property.m
@@ -46,3 +46,12 @@
 @synthesize z;  // suppressed
 @end
 
+// rdar://problem/10904479
+// Don't crash.
+@interface Test2
+// Minor FIXME: kill the redundant error
+@property (strong) UndeclaredClass *test2;  // expected-error {{unknown type name 'UndeclaredClass'}} expected-error {{must be of object type}}
+@end
+@implementation Test2
+@synthesize test2;
+@end