diff --git a/SDWebImage/SDWebImagePrefetcher.m b/SDWebImage/SDWebImagePrefetcher.m
index 7855eea..5c69a28 100644
--- a/SDWebImage/SDWebImagePrefetcher.m
+++ b/SDWebImage/SDWebImagePrefetcher.m
@@ -94,6 +94,7 @@
                 self.completionBlock(self.finishedCount, self.skippedCount);
                 self.completionBlock = nil;
             }
+            self.progressBlock = nil;
         }
     }];
 }