diff --git a/conservancy_beancount/rtutil.py b/conservancy_beancount/rtutil.py
index 0d87b9d1800bb02a1841f1c0ad25440d5aebcece..db2a5e2ad2e2ad97b6103f2f09d71e9a84a0b497 100644
--- a/conservancy_beancount/rtutil.py
+++ b/conservancy_beancount/rtutil.py
@@ -100,8 +100,9 @@ class RT:
     def exists(self, ticket_id: RTId, attachment_id: Optional[RTId]=None) -> bool:
         return self.url(ticket_id, attachment_id) is not None
 
-    def parse(self, s: str) -> Optional[Tuple[str, Optional[str]]]:
-        for regexp in self.PARSE_REGEXPS:
+    @classmethod
+    def parse(cls, s: str) -> Optional[Tuple[str, Optional[str]]]:
+        for regexp in cls.PARSE_REGEXPS:
             match = regexp.match(s)
             if match is not None:
                 ticket_id, attachment_id = match.groups()