diff -r 815c63526d1d -r edaae3616ba3 mercurial/bookmarks.py
--- a/mercurial/bookmarks.py	Sat Feb 15 15:06:41 2020 -0500
+++ b/mercurial/bookmarks.py	Sat Feb 15 14:51:33 2020 -0500
@@ -173,6 +173,8 @@
             nrefs.sort()
 
     def _del(self, mark):
+        if mark not in self._refmap:
+            return
         self._clean = False
         node = self._refmap.pop(mark)
         nrefs = self._nodemap[node]