diff --git a/reviewboard/diffviewer/managers.py b/reviewboard/diffviewer/managers.py
index 326a70f0be19d8b8544bf694ce1463aa6ea9f639..3d98b64b418a126771e853bd79b8074ac8710c81 100644
--- a/reviewboard/diffviewer/managers.py
+++ b/reviewboard/diffviewer/managers.py
@@ -41,7 +41,7 @@ class FileDiffManager(models.Manager):
         total_diff_size = 0
         total_bytes_saved = 0
 
-        for filediff in filediffs:
+        for filediff in filediffs.iterator():
             total_diffs_migrated += 1
 
             diff_size = len(filediff.diff64)