diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2763,7 +2763,9 @@ def buildcommittext(repo, ctx, subs, ext
 
     return "\n".join(edittext)
 
-def commitstatus(repo, node, branch, bheads=None, opts={}):
+def commitstatus(repo, node, branch, bheads=None, opts=None):
+    if opts is None:
+        opts = {}
     ctx = repo[node]
     parents = ctx.parents()