diff --git a/project.py b/project.py
index 6217aec8..1e525b38 100644
--- a/project.py
+++ b/project.py
@@ -1836,6 +1836,8 @@ class Project(object):
       cmd.append('--quiet')
     if not self.worktree:
       cmd.append('--update-head-ok')
+    if self.manifest.IsMirror:
+      cmd.append('--prune')
     cmd.append(name)
 
     # If using depth then we should not get all the tags since they may