--- a/mercurial/filelog.py	Mon Apr 30 15:32:11 2018 -0700
+++ b/mercurial/filelog.py	Thu Nov 30 21:19:46 2017 -0500
@@ -135,7 +135,9 @@
             return False
         t = self.revision(node)
         m = revlog.parsemeta(t)[0]
-        if m and "copy" in m:
+        # copy and copyrev occur in pairs. In rare cases due to bugs,
+        # one can occur without the other.
+        if m and "copy" in m and "copyrev" in m:
             return (m["copy"], revlog.bin(m["copyrev"]))
         return False