diff --git a/packages/python/src/codespar/mandate.py b/packages/python/src/codespar/mandate.py
index 097623b..493b08e 100644
--- a/packages/python/src/codespar/mandate.py
+++ b/packages/python/src/codespar/mandate.py
@@ -182,7 +182,7 @@ def esc(member: str) -> str:
         return member.replace("\\", "\\\\").replace(",", "\\,")
 
     purposes = ",".join(esc(p) for p in sorted(fields.get("purposes") or []))
-    version = int(fields.get("format_version"))
+    version = int(fields.get("format_version") or 0)
     parts = [
         str(fields.get("format_version")),
         _s(fields.get("id")),