diff --git a/scrapy/pipelines/files.py b/scrapy/pipelines/files.py
index c5dbd307b..b1b8404bb 100644
--- a/scrapy/pipelines/files.py
+++ b/scrapy/pipelines/files.py
@@ -364,8 +364,9 @@ class FilesPipeline(MediaPipeline):
     def file_downloaded(self, response, request, info):
         path = self.file_path(request, response=response, info=info)
         buf = BytesIO(response.body)
-        self.store.persist_file(path, buf, info)
         checksum = md5sum(buf)
+        buf.seek(0)
+        self.store.persist_file(path, buf, info)
         return checksum
 
     def item_completed(self, results, item, info):