diff --git a/SDWebImage/SDWebImageDownloaderOperation.m b/SDWebImage/SDWebImageDownloaderOperation.m
index 65f9af24..52f7af9c 100644
--- a/SDWebImage/SDWebImageDownloaderOperation.m
+++ b/SDWebImage/SDWebImageDownloaderOperation.m
@@ -73,7 +73,7 @@
         {
 			if (self.progressBlock)
 			{
-				self.progressBlock(0, 0);
+				self.progressBlock(0, -1);
 			}
             [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStartNotification object:self];
         }