diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
index 7956cd1..0e0977a 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
@@ -30,7 +30,7 @@ public class HttpClientDownloader implements Downloader {
 
     private Logger logger = Logger.getLogger(getClass());
 
-    private int poolSize;
+    private int poolSize = 1;
 
     @Override
     public Page download(Request request, Task task) {