diff --git a/SDWebImage/SDWebImageDownloaderOperation.m b/SDWebImage/SDWebImageDownloaderOperation.m
index 6a158f4..d2f3732 100644
--- a/SDWebImage/SDWebImageDownloaderOperation.m
+++ b/SDWebImage/SDWebImageDownloaderOperation.m
@@ -112,11 +112,14 @@
 
 - (void)reset
 {
-    self.cancelBlock = nil;
-    self.completedBlock = nil;
-    self.progressBlock = nil;
-    self.connection = nil;
-	self.imageData = nil;
+    dispatch_async(dispatch_get_main_queue(), ^
+    {
+        self.cancelBlock = nil;
+        self.completedBlock = nil;
+        self.progressBlock = nil;
+        self.connection = nil;
+        self.imageData = nil;
+    });
 }
 
 - (void)setFinished:(BOOL)finished