diff --git a/SDWebImage/SDWebImageDownloaderOperation.m b/SDWebImage/SDWebImageDownloaderOperation.m
index 4bf2873..ff28345 100644
--- a/SDWebImage/SDWebImageDownloaderOperation.m
+++ b/SDWebImage/SDWebImageDownloaderOperation.m
@@ -206,7 +206,7 @@ NSString *const SDWebImageDownloadFinishNotification = @"SDWebImageDownloadFinis
 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
     
     //'304 Not Modified' is an exceptional one
-    if ((![response respondsToSelector:@selector(statusCode)] || [((NSHTTPURLResponse *)response) statusCode] < 400) && [((NSHTTPURLResponse *)response) statusCode] != 304) {
+    if (![response respondsToSelector:@selector(statusCode)] || ([((NSHTTPURLResponse *)response) statusCode] < 400 && [((NSHTTPURLResponse *)response) statusCode] != 304)) {
         NSInteger expected = response.expectedContentLength > 0 ? (NSInteger)response.expectedContentLength : 0;
         self.expectedSize = expected;
         if (self.progressBlock) {