diff --git a/master/buildbot/process/buildstep.py b/master/buildbot/process/buildstep.py
index <HASH>..<HASH> 100644
--- a/master/buildbot/process/buildstep.py
+++ b/master/buildbot/process/buildstep.py
@@ -57,6 +57,7 @@ from buildbot.process.results import SUCCESS
 from buildbot.process.results import WARNINGS
 from buildbot.process.results import Results
 from buildbot.process.results import worst_status
+from buildbot.util import bytes2NativeString
 from buildbot.util import debounce
 from buildbot.util import flatten
 from buildbot.worker_transition import WorkerAPICompatMixin
@@ -804,6 +805,7 @@ class BuildStep(results.ResultComputingConfigMixin,
         logid = yield self.master.data.updates.addLog(self.stepid,
                                                       util.ascii2unicode(name), u'h')
         l = self._newLog(name, u'h', logid)
+        html = bytes2NativeString(html)
         yield l.addContent(html)
         yield l.finish()
Make sure that html is a native string