diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -721,10 +721,12 @@ def rebase(ui, repo, **opts):
     finally:
         release(lock, wlock)
 
-def _definesets(ui, repo, destf=None, srcf=None, basef=None, revf=[],
+def _definesets(ui, repo, destf=None, srcf=None, basef=None, revf=None,
                 destspace=None):
     """use revisions argument to define destination and rebase set
     """
+    revf = revf or []
+
     # destspace is here to work around issues with `hg pull --rebase` see
     # issue5214 for details
     if srcf and basef: