diff --git a/SDWebImage/SDWebImageDownloader.m b/SDWebImage/SDWebImageDownloader.m
index 10cd983e..a3411cb9 100644
--- a/SDWebImage/SDWebImageDownloader.m
+++ b/SDWebImage/SDWebImageDownloader.m
@@ -160,6 +160,7 @@ static NSString *const kCompletedCallbackKey = @"completed";
             [wself.lastAddedOperation addDependency:operation];
             wself.lastAddedOperation = operation;
         }
+        operation = nil; // break retain cycle
     }];
 
     return operation;