diff -r 1df7e7b8558e -r 04c319a07c7b mercurial/scmutil.py
--- a/mercurial/scmutil.py	Sun Feb 25 22:30:14 2018 -0500
+++ b/mercurial/scmutil.py	Sun Feb 25 23:08:41 2018 -0500
@@ -208,7 +208,7 @@
             ui.warn(_("(%s)\n") % inst.hint)
     except ImportError as inst:
         ui.warn(_("abort: %s!\n") % inst)
-        m = str(inst).split()[-1]
+        m = util.forcebytestr(inst).split()[-1]
         if m in "mpatch bdiff".split():
             ui.warn(_("(did you forget to compile extensions?)\n"))
         elif m in "zlib".split():