diff --git a/SDWebImage/SDWebImageManager.m b/SDWebImage/SDWebImageManager.m
index 38f75f0..0d2f31b 100644
--- a/SDWebImage/SDWebImageManager.m
+++ b/SDWebImage/SDWebImageManager.m
@@ -194,7 +194,9 @@
 
                     if (error.code != NSURLErrorNotConnectedToInternet && error.code != NSURLErrorCancelled && error.code != NSURLErrorTimedOut) {
                         @synchronized (self.failedURLs) {
-                            [self.failedURLs addObject:url];
+                            if (![self.failedURLs containsObject:url]) {
+                                [self.failedURLs addObject:url];
+                            }
                         }
                     }
                 }