diff --git a/lib/cmdlib.py b/lib/cmdlib.py
index 1ab20ac9203091a47f3951dd3f5855cda3cc64c4..f034c1e16ddd81b8dbbf0316c27c9104b218fef2 100644
--- a/lib/cmdlib.py
+++ b/lib/cmdlib.py
@@ -5382,7 +5382,8 @@ class LUReplaceDisks(LogicalUnit):
                     new_net_id)
       new_drbd = objects.Disk(dev_type=constants.LD_DRBD8,
                               logical_id=new_alone_id,
-                              children=dev.children)
+                              children=dev.children,
+                              size=dev.size)
       try:
         _CreateSingleBlockDev(self, new_node, instance, new_drbd,
                               _GetInstanceInfoText(instance), False)