diff --git a/SDWebImage/SDWebImagePrefetcher.m b/SDWebImage/SDWebImagePrefetcher.m
index e1c188c9..c029e8d9 100644
--- a/SDWebImage/SDWebImagePrefetcher.m
+++ b/SDWebImage/SDWebImagePrefetcher.m
@@ -17,7 +17,7 @@
 @property (assign, nonatomic) NSUInteger skippedCount;
 @property (assign, nonatomic) NSUInteger finishedCount;
 @property (assign, nonatomic) NSTimeInterval startedTime;
-@property (SDDispatchQueueSetterSementics, nonatomic) void (^completionBlock)(NSUInteger, NSUInteger);
+@property (copy, nonatomic) void (^completionBlock)(NSUInteger, NSUInteger);
 
 @end