diff --git a/ocfl/object.py b/ocfl/object.py
index adc1334..f22c149 100755
--- a/ocfl/object.py
+++ b/ocfl/object.py
@@ -485,7 +485,9 @@ def add_version_with_content(self, objdir="", srcdir=None, metadata=None):
         # Write the new version
         return self.commit_new_version(new_version)
 
-    def start_new_version(self, objdir=None, srcdir="",
+    def start_new_version(self, *,
+                          objdir=None,
+                          srcdir="",
                           digest_algorithm=None,
                           fixity=None,
                           metadata=None,