diff --git a/HSDownloadManager/HSDownloadManager.m b/HSDownloadManager/HSDownloadManager.m
index 892fdb2..0fe1a28 100644
--- a/HSDownloadManager/HSDownloadManager.m
+++ b/HSDownloadManager/HSDownloadManager.m
@@ -310,7 +310,9 @@ - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)data
     NSUInteger expectedSize = sessionModel.totalLength;
     CGFloat progress = 1.0 * receivedSize / expectedSize;
 
-    sessionModel.progressBlock(receivedSize, expectedSize, progress);
+    if (sessionModel) {
+        sessionModel.progressBlock(receivedSize, expectedSize, progress);
+    }
 }
 
 /**