diff --git a/dom0/aux-tools/block_cleaner_daemon.py b/dom0/aux-tools/block_cleaner_daemon.py
index 76154759..75b549dc 100755
--- a/dom0/aux-tools/block_cleaner_daemon.py
+++ b/dom0/aux-tools/block_cleaner_daemon.py
@@ -35,7 +35,7 @@ def handle_vbd_state(path):
             vm_xid = path_components[6]
             vm_dev = path_components[7]
             if vm_xid in domain_list:
-                subprocess.call('xl', 'block-detach', vm_xid, vm_dev)
+                subprocess.call(['xl', 'block-detach', vm_xid, vm_dev])
 
 def main():