diff --git a/project.py b/project.py
index d12d466..281ba4b 100755
--- a/project.py
+++ b/project.py
@@ -2252,7 +2252,10 @@
       spec.append('tag')
       spec.append(tag_name)
 
-    branch = self.revisionExpr
+    if self.manifest.IsMirror and not current_branch_only:
+      branch = None
+    else:
+      branch = self.revisionExpr
     if (not self.manifest.IsMirror and is_sha1 and depth
         and git_require((1, 8, 3))):
       # Shallow checkout of a specific commit, fetch from that commit and not