diff --git a/kafka/tools/assigner/sizers/prometheus.py b/kafka/tools/assigner/sizers/prometheus.py
index 457ab8d..1eb41c3 100644
--- a/kafka/tools/assigner/sizers/prometheus.py
+++ b/kafka/tools/assigner/sizers/prometheus.py
@@ -83,6 +83,9 @@ def _parse_prometheus_metric(self, text):
         return metric or None
 
     def _get_prometheus_metrics(self, hostname, port, path):
+        # When hostname is an ipv6 addr, add brackets to separate addr from port
+        if hostname.count(':') >= 2 and hostname[0] != '[' and hostname[-1] != ']':
+            hostname = '[{}]'.format(hostname)
         url = 'http://{}:{}{}'.format(hostname, port, path)
         body = ''
         try:
diff --git a/tests/tools/assigner/sizers/test_prometheus.py b/tests/tools/assigner/sizers/test_prometheus.py
index a2f4432..5ee1e75 100644
--- a/tests/tools/assigner/sizers/test_prometheus.py
+++ b/tests/tools/assigner/sizers/test_prometheus.py
@@ -159,6 +159,23 @@ def test_sizer_get_prometheus_metrics_200(self, mock_urlopen):
         metrics = sizer._get_prometheus_metrics('localhost', 1234, '/metrics')
         self.assertSequenceEqual(metrics, ['404 not found'])
 
+    @patch('kafka.tools.assigner.sizers.prometheus.urlopen')
+    def test_sizer_get_prometheus_metrics_ipv6(self, mock_urlopen):
+        test_paths = [
+            ('1.2.3.4', '1.2.3.4'),
+            ('username:password@example.com', 'username:password@example.com'),
+            ('::1', '[::1]'),
+            ('[2001:db8::1]', '[2001:db8::1]'),
+        ]
+        for before, after in test_paths:
+            m = Mock()
+            m.getcode.return_value = 200
+            mock_urlopen.return_value = m
+            sizer = SizerPrometheus(self.args, self.cluster)
+            sizer._get_prometheus_metrics(before, 1234, '/metrics')
+            mock_urlopen.assert_called_once_with('http://{}:1234/metrics'.format(after))
+            mock_urlopen.reset_mock()
+
     @patch('kafka.tools.assigner.sizers.prometheus.urlopen')
     def test_sizer_get_prometheus_metrics_404(self, mock_urlopen):
         m = Mock()