diff --git a/subcmds/rebase.py b/subcmds/rebase.py
index b9a7774..1bdc1f0 100644
--- a/subcmds/rebase.py
+++ b/subcmds/rebase.py
@@ -62,6 +62,9 @@
     if opt.interactive and not one_project:
       print('error: interactive rebase not supported with multiple projects',
             file=sys.stderr)
+      if len(args) == 1:
+        print('note: project %s is mapped to more than one path' % (args[0],),
+            file=sys.stderr)
       return -1
 
     for project in all_projects: