diff --git a/fail2ban/client/fail2banregex.py b/fail2ban/client/fail2banregex.py
index 29723dfb..87d359ba 100644
--- a/fail2ban/client/fail2banregex.py
+++ b/fail2ban/client/fail2banregex.py
@@ -694,6 +694,14 @@ def exec_command_line(*args):
 	stdout.setFormatter(Formatter(getVerbosityFormat(opts.verbose, fmt)))
 	logSys.addHandler(stdout)
 
-	fail2banRegex = Fail2banRegex(opts)
+	try:
+		fail2banRegex = Fail2banRegex(opts)
+	except Exception as e:
+		if opts.verbose or logSys.getEffectiveLevel()<=logging.DEBUG:
+			logSys.critical(e, exc_info=True)
+		else:
+			output( 'ERROR: %s' % e )
+		sys.exit(255)
+
 	if not fail2banRegex.start(args):
 		sys.exit(255)
diff --git a/fail2ban/server/datetemplate.py b/fail2ban/server/datetemplate.py
index e032c2b0..d827cd1a 100644
--- a/fail2ban/server/datetemplate.py
+++ b/fail2ban/server/datetemplate.py
@@ -301,14 +301,17 @@ class DatePatternRegex(DateTemplate):
 		if wordBegin and RE_EXLINE_BOUND_BEG.search(pattern):
 			pattern = RE_EXLINE_BOUND_BEG.sub('', pattern)
 			wordBegin = 'start'
-		# wrap to regex:
-		fmt = self._patternRE.sub(r'%(\1)s', pattern)
-		self.name = fmt % self._patternName
-		regex = fmt % timeRE
-		# if expected add (?iu) for "ignore case" and "unicode":
-		if RE_ALPHA_PATTERN.search(pattern):
-			regex = r'(?iu)' + regex
-		super(DatePatternRegex, self).setRegex(regex, wordBegin, wordEnd)
+		try:
+			# wrap to regex:
+			fmt = self._patternRE.sub(r'%(\1)s', pattern)
+			self.name = fmt % self._patternName
+			regex = fmt % timeRE
+			# if expected add (?iu) for "ignore case" and "unicode":
+			if RE_ALPHA_PATTERN.search(pattern):
+				regex = r'(?iu)' + regex
+			super(DatePatternRegex, self).setRegex(regex, wordBegin, wordEnd)
+		except Exception as e:
+			raise TypeError("Failed to set datepattern '%s' (may be an invalid format or unescaped percent char): %s" % (pattern, e))
 
 	def getDate(self, line, dateMatch=None, default_tz=None):
 		"""Method to return the date for a log line.
diff --git a/fail2ban/tests/fail2banregextestcase.py b/fail2ban/tests/fail2banregextestcase.py
index 44acfd35..aa6977ed 100644
--- a/fail2ban/tests/fail2banregextestcase.py
+++ b/fail2ban/tests/fail2banregextestcase.py
@@ -368,3 +368,16 @@ class Fail2banRegexTest(LogCaptureTestCase):
 			r"Authentication failure"
 		), 0)
 		self.assertLogged('No failure-id group in ')
+
+	def testExecCmdLine_ErrorParam(self):
+		# single line error:
+		self.assertNotEqual(_test_exec_command_line(
+			'-l', 'notice', '-d', '%:%.%-', 'LOG', 'RE'
+		), 0)
+		self.assertLogged('ERROR: Failed to set datepattern')
+		# verbose (traceback/callstack):
+		self.pruneLog()
+		self.assertNotEqual(_test_exec_command_line(
+			'-v', '-d', '%:%.%-', 'LOG', 'RE'
+		), 0)
+		self.assertLogged('Failed to set datepattern')