--- a/mercurial/revlog.py	Mon Sep 24 22:32:30 2018 -0400
+++ b/mercurial/revlog.py	Tue Sep 25 22:19:40 2018 +0900
@@ -1325,7 +1325,7 @@
         def isvalid(prefix):
             try:
                 node = self._partialmatch(prefix)
-            except error.RevlogError:
+            except error.AmbiguousPrefixLookupError:
                 return False
             except error.WdirUnsupported:
                 # single 'ff...' match