diff --git a/SDWebImage/SDWebImageDownloaderOperation.m b/SDWebImage/SDWebImageDownloaderOperation.m
index 05783f8..baced7c 100644
--- a/SDWebImage/SDWebImageDownloaderOperation.m
+++ b/SDWebImage/SDWebImageDownloaderOperation.m
@@ -129,6 +129,7 @@
 }
 
 - (void)cancelInternalAndStop {
+    if (self.isFinished) return;
     [self cancelInternal];
     CFRunLoopStop(CFRunLoopGetCurrent());
 }