diff --git a/contrib/python3-whitelist b/contrib/python3-whitelist
--- a/contrib/python3-whitelist
+++ b/contrib/python3-whitelist
@@ -44,6 +44,7 @@
 test-branch-option.t
 test-branch-tag-confict.t
 test-branches.t
+test-bugzilla.t
 test-bundle-phases.t
 test-bundle-r.t
 test-bundle-type.t
diff --git a/hgext/bugzilla.py b/hgext/bugzilla.py
--- a/hgext/bugzilla.py
+++ b/hgext/bugzilla.py
@@ -303,6 +303,7 @@
     error,
     logcmdutil,
     mail,
+    pycompat,
     registrar,
     url,
     util,
@@ -342,10 +343,10 @@
     default='bugs',
 )
 configitem('bugzilla', 'fixregexp',
-    default=(r'fix(?:es)?\s*(?:bugs?\s*)?,?\s*'
-             r'(?:nos?\.?|num(?:ber)?s?)?\s*'
-             r'(?P<ids>(?:#?\d+\s*(?:,?\s*(?:and)?)?\s*)+)'
-             r'\.?\s*(?:h(?:ours?)?\s*(?P<hours>\d*(?:\.\d+)?))?')
+    default=(br'fix(?:es)?\s*(?:bugs?\s*)?,?\s*'
+             br'(?:nos?\.?|num(?:ber)?s?)?\s*'
+             br'(?P<ids>(?:#?\d+\s*(?:,?\s*(?:and)?)?\s*)+)'
+             br'\.?\s*(?:h(?:ours?)?\s*(?P<hours>\d*(?:\.\d+)?))?')
 )
 configitem('bugzilla', 'fixresolution',
     default='FIXED',
@@ -363,9 +364,9 @@
     default=None,
 )
 configitem('bugzilla', 'regexp',
-    default=(r'bugs?\s*,?\s*(?:#|nos?\.?|num(?:ber)?s?)?\s*'
-             r'(?P<ids>(?:\d+\s*(?:,?\s*(?:and)?)?\s*)+)'
-             r'\.?\s*(?:h(?:ours?)?\s*(?P<hours>\d*(?:\.\d+)?))?')
+    default=(br'bugs?\s*,?\s*(?:#|nos?\.?|num(?:ber)?s?)?\s*'
+             br'(?P<ids>(?:\d+\s*(?:,?\s*(?:and)?)?\s*)+)'
+             br'\.?\s*(?:h(?:ours?)?\s*(?P<hours>\d*(?:\.\d+)?))?')
 )
 configitem('bugzilla', 'strip',
     default=0,
@@ -733,7 +734,7 @@
         c = self.bzproxy.Bug.comments({'ids': [id],
                                        'include_fields': ['text'],
                                        'token': self.bztoken})
-        return ''.join([t['text'] for t in c['bugs'][str(id)]['comments']])
+        return ''.join([t['text'] for t in c['bugs']['%d' % id]['comments']])
 
     def filter_real_bug_ids(self, bugs):
         probe = self.bzproxy.Bug.get({'ids': sorted(bugs.keys()),
@@ -804,11 +805,11 @@
 
     def makecommandline(self, fieldname, value):
         if self.bzvermajor >= 4:
-            return "@%s %s" % (fieldname, str(value))
+            return "@%s %s" % (fieldname, pycompat.bytestr(value))
         else:
             if fieldname == "id":
                 fieldname = "bug_id"
-            return "@%s = %s" % (fieldname, str(value))
+            return "@%s = %s" % (fieldname, pycompat.bytestr(value))
 
     def send_bug_modify_email(self, bugid, commands, comment, committer):
         '''send modification message to Bugzilla bug via email.
@@ -873,7 +874,7 @@
         self.fixresolution = self.ui.config('bugzilla', 'fixresolution')
 
     def apiurl(self, targets, include_fields=None):
-        url = '/'.join([self.bzroot] + [str(t) for t in targets])
+        url = '/'.join([self.bzroot] + [pycompat.bytestr(t) for t in targets])
         qv = {}
         if self.apikey:
             qv['api_key'] = self.apikey
@@ -938,7 +939,7 @@
         for bugid in bugs.keys():
             burl = self.apiurl(('bug', bugid, 'comment'), include_fields='text')
             result = self._fetch(burl)
-            comments = result['bugs'][str(bugid)]['comments']
+            comments = result['bugs'][pycompat.bytestr(bugid)]['comments']
             if any(sn in c['text'] for c in comments):
                 self.ui.status(_('bug %d already knows about changeset %s\n') %
                                (bugid, sn))
@@ -1011,7 +1012,7 @@
             self.ui.config('bugzilla', 'regexp'), re.IGNORECASE)
         self.fix_re = re.compile(
             self.ui.config('bugzilla', 'fixregexp'), re.IGNORECASE)
-        self.split_re = re.compile(r'\D+')
+        self.split_re = re.compile(br'\D+')
 
     def find_bugs(self, ctx):
         '''return bugs dictionary created from commit comment.
@@ -1098,7 +1099,7 @@
         t = logcmdutil.changesettemplater(self.ui, self.repo, spec)
         self.ui.pushbuffer()
         t.show(ctx, changes=ctx.changeset(),
-               bug=str(bugid),
+               bug=pycompat.bytestr(bugid),
                hgweb=self.ui.config('web', 'baseurl'),
                root=self.repo.root,
                webroot=webroot(self.repo.root))
diff --git a/tests/test-bugzilla.t b/tests/test-bugzilla.t
--- a/tests/test-bugzilla.t
+++ b/tests/test-bugzilla.t
@@ -3,7 +3,9 @@
   $ cat <<EOF > bzmock.py
   > from __future__ import absolute_import
   > from mercurial import extensions
+  > from mercurial import pycompat
   > from mercurial import registrar
+  > from mercurial.utils import stringutil
   > 
   > configtable = {}
   > configitem = registrar.configitem(configtable)
@@ -18,14 +20,17 @@
   >             super(bzmock, self).__init__(ui)
   >             self._logfile = ui.config(b'bugzilla', b'mocklog')
   >         def updatebug(self, bugid, newstate, text, committer):
-  >             with open(self._logfile, 'a') as f:
-  >                 f.write('update bugid=%r, newstate=%r, committer=%r\n'
-  >                         % (bugid, newstate, committer))
-  >                 f.write('----\n' + text + '\n----\n')
+  >             with open(pycompat.fsdecode(self._logfile), 'ab') as f:
+  >                 f.write(b'update bugid=%s, newstate=%s, committer=%s\n'
+  >                         % (stringutil.pprint(bugid),
+  >                            stringutil.pprint(newstate),
+  >                            stringutil.pprint(committer)))
+  >                 f.write(b'----\n' + text + b'\n----\n')
   >         def notify(self, bugs, committer):
-  >             with open(self._logfile, 'a') as f:
-  >                 f.write('notify bugs=%r, committer=%r\n'
-  >                         % (bugs, committer))
+  >             with open(pycompat.fsdecode(self._logfile), 'ab') as f:
+  >                 f.write(b'notify bugs=%s, committer=%s\n'
+  >                         % (stringutil.pprint(bugs),
+  >                            stringutil.pprint(committer)))
   >     bugzilla.bugzilla._versions[b'mock'] = bzmock
   > EOF