diff --git a/mercurial/mergestate.py b/mercurial/mergestate.py
--- a/mercurial/mergestate.py
+++ b/mercurial/mergestate.py
@@ -53,8 +53,6 @@
 
 RECORD_MERGE_DRIVER_STATE = b'm'
 RECORD_OVERRIDE = b't'
-RECORD_UNSUPPORTED_MANDATORY = b'X'
-RECORD_UNSUPPORTED_ADVISORY = b'x'
 
 MERGE_DRIVER_STATE_UNMARKED = b'u'
 MERGE_DRIVER_STATE_MARKED = b'm'