diff --git a/AFNetworking/UIImageView+AFNetworking.m b/AFNetworking/UIImageView+AFNetworking.m
index 6de959f..70bd401 100644
--- a/AFNetworking/UIImageView+AFNetworking.m
+++ b/AFNetworking/UIImageView+AFNetworking.m
@@ -59,10 +59,11 @@ static char kAFImageRequestOperationObjectKey;
 + (NSOperationQueue *)af_sharedImageRequestOperationQueue {
     static NSOperationQueue *_af_imageRequestOperationQueue = nil;
     
-    if (!_af_imageRequestOperationQueue) {
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
         _af_imageRequestOperationQueue = [[NSOperationQueue alloc] init];
-        [_af_imageRequestOperationQueue setMaxConcurrentOperationCount:8];
-    }
+        [_af_imageRequestOperationQueue setMaxConcurrentOperationCount:NSOperationQueueDefaultMaxConcurrentOperationCount];
+    });
     
     return _af_imageRequestOperationQueue;
 }