diff --git a/bob/bio/base/database/database.py b/bob/bio/base/database/database.py
index 4867bd4352ac6d334fadf2bed1ad8efcb814c66b..72c0af89bb18abb3d5a3b587315c1bc44db2fb8b 100644
--- a/bob/bio/base/database/database.py
+++ b/bob/bio/base/database/database.py
@@ -294,7 +294,7 @@ class BioDatabase(six.with_metaclass(abc.ABCMeta, bob.db.base.FileDatabase)):
         raise NotImplementedError("Please implement this function in derived classes")
 
 
-    def groups(self):
+    def groups(self, protocol=None):
         """
         Returns the names of all registered groups in the database