diff --git a/NSObject+Attachment.h b/NSObject+Attachment.h
index 8a3b50b..45b51af 100644
--- a/NSObject+Attachment.h
+++ b/NSObject+Attachment.h
@@ -9,6 +9,6 @@
 
 @interface NSObject (Attachment)
 
-@property (nonatomic, strong) id attachment;
+@property (atomic, strong) id attachment;
 
 @end