diff --git a/fail2ban/helpers.py b/fail2ban/helpers.py
index 5c1750a6..de8a2794 100644
--- a/fail2ban/helpers.py
+++ b/fail2ban/helpers.py
@@ -98,6 +98,8 @@ if sys.version_info >= (3,): # pragma: 2.x no cover
 		if not isinstance(x, bytes):
 			return str(x)
 		return x.decode(PREFER_ENC, 'replace')
+	def uni_bytes(x):
+		return bytes(x, 'UTF-8')
 else: # pragma: 3.x no cover
 	def uni_decode(x, enc=PREFER_ENC, errors='strict'):
 		try:
@@ -115,6 +117,7 @@ else: # pragma: 3.x no cover
 			return x.encode(PREFER_ENC, 'replace')
 	else:
 		uni_string = str
+	uni_bytes = bytes
 
 
 def _as_bool(val):
diff --git a/fail2ban/tests/filtertestcase.py b/fail2ban/tests/filtertestcase.py
index 4e308e38..9fea84af 100644
--- a/fail2ban/tests/filtertestcase.py
+++ b/fail2ban/tests/filtertestcase.py
@@ -36,6 +36,7 @@ try:
 except ImportError:
 	journal = None
 
+from ..helpers import uni_bytes
 from ..server.jail import Jail
 from ..server.filterpoll import FilterPoll
 from ..server.filter import FailTicket, Filter, FileFilter, FileContainer
@@ -109,6 +110,7 @@ class _tmSerial():
 		return "%s%02u" % (c._str_s, sec)
 
 _tm = _tmSerial._tm
+_tmb = lambda t: uni_bytes(_tm(t))
 
 
 def _assert_equal_entries(utest, found, output, count=None):
@@ -204,6 +206,8 @@ def _copy_lines_between_files(in_, fout, n=None, skip=0, mode='a', terminal_line
 	# on old Python st_mtime is int, so we should give at least 1 sec so
 	# polling filter could detect the change
 	mtimesleep()
+	if terminal_line is not None:
+		terminal_line = uni_bytes(terminal_line)
 	if isinstance(in_, str): # pragma: no branch - only used with str in test cases
 		fin = open(in_, 'rb')
 	else:
@@ -213,18 +217,21 @@ def _copy_lines_between_files(in_, fout, n=None, skip=0, mode='a', terminal_line
 		fin.readline()
 	# Read
 	i = 0
-	if not lines: lines = []
+	if lines:
+		lines = map(uni_bytes, lines)
+	else:
+		lines = []
 	while n is None or i < n:
-		l = fin.readline().decode('UTF-8', 'replace').rstrip('\r\n')
+		l = fin.readline().rstrip(b'\r\n')
 		if terminal_line is not None and l == terminal_line:
 			break
 		lines.append(l)
 		i += 1
 	# Write: all at once and flush
 	if isinstance(fout, str):
-		fout = open(fout, mode)
+		fout = open(fout, mode+'b')
 	DefLogSys.debug('  ++ write %d test lines', len(lines))
-	fout.write('\n'.join(lines)+'\n')
+	fout.write(b'\n'.join(lines)+b'\n')
 	fout.flush()
 	if isinstance(in_, str): # pragma: no branch - only used with str in test cases
 		# Opened earlier, therefore must close it
@@ -711,7 +718,7 @@ class LogFileFilterPoll(unittest.TestCase):
 		self.filter.setDatePattern(r'^%ExY-%Exm-%Exd %ExH:%ExM:%ExS')
 		fname = tempfile.mktemp(prefix='tmp_fail2ban', suffix='.log')
 		time = 1417512352
-		f = open(fname, 'w')
+		f = open(fname, 'wb')
 		fc = None
 		try:
 			fc = FileContainer(fname, self.filter.getLogEncoding())
@@ -722,7 +729,7 @@ class LogFileFilterPoll(unittest.TestCase):
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 0)
 			# one entry with exact time:
-			f.write("%s [sshd] error: PAM: failure len 1\n" % _tm(time))
+			f.write(b"%s [sshd] error: PAM: failure len 1\n" % _tmb(time))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 
@@ -734,7 +741,7 @@ class LogFileFilterPoll(unittest.TestCase):
 			fc.open()
 			# no time - nothing should be found :
 			for i in xrange(10):
-				f.write("[sshd] error: PAM: failure len 1\n")
+				f.write(b"[sshd] error: PAM: failure len 1\n")
 				f.flush()
 				fc.setPos(0); self.filter.seekToTime(fc, time)
 
@@ -745,38 +752,38 @@ class LogFileFilterPoll(unittest.TestCase):
 			fc = FileContainer(fname, self.filter.getLogEncoding())
 			fc.open()
 			# one entry with smaller time:
-			f.write("%s [sshd] error: PAM: failure len 2\n" % _tm(time - 10))
+			f.write(b"%s [sshd] error: PAM: failure len 2\n" % _tmb(time - 10))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 53)
 			# two entries with smaller time:
-			f.write("%s [sshd] error: PAM: failure len 3 2 1\n" % _tm(time - 9))
+			f.write(b"%s [sshd] error: PAM: failure len 3 2 1\n" % _tmb(time - 9))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 110)
 			# check move after end (all of time smaller):
-			f.write("%s [sshd] error: PAM: failure\n" % _tm(time - 1))
+			f.write(b"%s [sshd] error: PAM: failure\n" % _tmb(time - 1))
 			f.flush()
 			self.assertEqual(fc.getFileSize(), 157)
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 157)
 
 			# stil one exact line:
-			f.write("%s [sshd] error: PAM: Authentication failure\n" % _tm(time))
-			f.write("%s [sshd] error: PAM: failure len 1\n" % _tm(time))
+			f.write(b"%s [sshd] error: PAM: Authentication failure\n" % _tmb(time))
+			f.write(b"%s [sshd] error: PAM: failure len 1\n" % _tmb(time))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 157)
 
 			# add something hereafter:
-			f.write("%s [sshd] error: PAM: failure len 3 2 1\n" % _tm(time + 2))
-			f.write("%s [sshd] error: PAM: Authentication failure\n" % _tm(time + 3))
+			f.write(b"%s [sshd] error: PAM: failure len 3 2 1\n" % _tmb(time + 2))
+			f.write(b"%s [sshd] error: PAM: Authentication failure\n" % _tmb(time + 3))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 157)
 			# add something hereafter:
-			f.write("%s [sshd] error: PAM: failure\n" % _tm(time + 9))
-			f.write("%s [sshd] error: PAM: failure len 4 3 2\n" % _tm(time + 9))
+			f.write(b"%s [sshd] error: PAM: failure\n" % _tmb(time + 9))
+			f.write(b"%s [sshd] error: PAM: failure len 4 3 2\n" % _tmb(time + 9))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 157)
@@ -797,7 +804,7 @@ class LogFileFilterPoll(unittest.TestCase):
 		self.filter.setDatePattern(r'^%ExY-%Exm-%Exd %ExH:%ExM:%ExS')
 		fname = tempfile.mktemp(prefix='tmp_fail2ban', suffix='.log')
 		time = 1417512352
-		f = open(fname, 'w')
+		f = open(fname, 'wb')
 		fc = None
 		count = 1000 if unittest.F2B.fast else 10000
 		try:
@@ -808,14 +815,14 @@ class LogFileFilterPoll(unittest.TestCase):
 			# write lines with smaller as search time:
 			t = time - count - 1
 			for i in xrange(count):
-				f.write("%s [sshd] error: PAM: failure\n" % _tm(t))
+				f.write(b"%s [sshd] error: PAM: failure\n" % _tmb(t))
 				t += 1
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 47*count)
 			# write lines with exact search time:
 			for i in xrange(10):
-				f.write("%s [sshd] error: PAM: failure\n" % _tm(time))
+				f.write(b"%s [sshd] error: PAM: failure\n" % _tmb(time))
 			f.flush()
 			fc.setPos(0); self.filter.seekToTime(fc, time)
 			self.assertEqual(fc.getPos(), 47*count)
@@ -825,7 +832,7 @@ class LogFileFilterPoll(unittest.TestCase):
 			t = time+1
 			for i in xrange(count//500):
 				for j in xrange(500):
-					f.write("%s [sshd] error: PAM: failure\n" % _tm(t))
+					f.write(b"%s [sshd] error: PAM: failure\n" % _tmb(t))
 					t += 1
 				f.flush()
 				fc.setPos(0); self.filter.seekToTime(fc, time)
@@ -847,7 +854,7 @@ class LogFileMonitor(LogCaptureTestCase):
 		LogCaptureTestCase.setUp(self)
 		self.filter = self.name = 'NA'
 		_, self.name = tempfile.mkstemp('fail2ban', 'monitorfailures')
-		self.file = open(self.name, 'a')
+		self.file = open(self.name, 'ab')
 		self.filter = FilterPoll(DummyJail())
 		self.filter.addLogPath(self.name, autoSeek=False)
 		self.filter.active = True
@@ -899,7 +906,7 @@ class LogFileMonitor(LogCaptureTestCase):
 		_org_processLine = self.filter.processLine
 		self.filter.processLine = None
 		for i in range(100):
-			self.file.write("line%d\n" % 1)
+			self.file.write(b"line%d\n" % 1)
 		self.file.flush()
 		for i in range(100):
 			self.filter.getFailures(self.name)
@@ -910,7 +917,7 @@ class LogFileMonitor(LogCaptureTestCase):
 		self.filter.idle = False
 		self.filter.getFailures(self.name)
 		self.filter.processLine = _org_processLine
-		self.file.write("line%d\n" % 1)
+		self.file.write(b"line%d\n" % 1)
 		self.file.flush()
 		self.filter.getFailures(self.name)
 		self.assertNotLogged('Failed to process line:')
@@ -934,7 +941,7 @@ class LogFileMonitor(LogCaptureTestCase):
 		mtimesleep()				# to guarantee freshier mtime
 		for i in range(4):			  # few changes
 			# unless we write into it
-			self.file.write("line%d\n" % i)
+			self.file.write(b"line%d\n" % i)
 			self.file.flush()
 			self.assertTrue(self.isModified())
 			self.assertTrue(self.notModified())
@@ -943,11 +950,11 @@ class LogFileMonitor(LogCaptureTestCase):
 		# we are not signaling as modified whenever
 		# it gets away
 		self.assertTrue(self.notModified(1))
-		f = open(self.name, 'a')
+		f = open(self.name, 'ab')
 		self.assertTrue(self.isModified())
 		self.assertTrue(self.notModified())
 		mtimesleep()
-		f.write("line%d\n" % i)
+		f.write(b"line%d\n" % i)
 		f.flush()
 		self.assertTrue(self.isModified())
 		self.assertTrue(self.notModified())
@@ -1077,7 +1084,7 @@ def get_monitor_failures_testcase(Filter_):
 			self.filter = self.name = 'NA'
 			self.name = '%s-%d' % (testclass_name, self.count)
 			MonitorFailures.count += 1 # so we have unique filenames across tests
-			self.file = open(self.name, 'a')
+			self.file = open(self.name, 'ab')
 			self.jail = DummyJail()
 			self.filter = Filter_(self.jail)
 			# mock-up common error to find catched unhandled exceptions: