sonlinux
diff --git a/‎prometheus_client/core.py
Lines changed: 4 additions & 4 deletions b/‎prometheus_client/core.py
Lines changed: 4 additions & 4 deletions
diff --git a/‎tests/test_core.py
Lines changed: 10 additions & 0 deletions b/‎tests/test_core.py
Lines changed: 10 additions & 0 deletions
@@ -187,7 +187,7 @@ def __init__(self, name, documentation, value=None, labels=None):
             raise ValueError('Can only specify at most one of value and labels.')
         if labels is None:
           labels = []
-        self._labelnames = labels
+        self._labelnames = tuple(labels)
         if value is not None:
           self.add_metric([], value)
 
@@ -212,7 +212,7 @@ def __init__(self, name, documentation, value=None, labels=None):
             raise ValueError('Can only specify at most one of value and labels.')
         if labels is None:
           labels = []
-        self._labelnames = labels
+        self._labelnames = tuple(labels)
         if value is not None:
           self.add_metric([], value)
 
@@ -239,7 +239,7 @@ def __init__(self, name, documentation, count_value=None, sum_value=None, labels
             raise ValueError('Can only specify at most one of value and labels.')
         if labels is None:
           labels = []
-        self._labelnames = labels
+        self._labelnames = tuple(labels)
         if count_value is not None:
           self.add_metric([], count_value, sum_value)
 
@@ -268,7 +268,7 @@ def __init__(self, name, documentation, buckets=None, sum_value=None, labels=Non
             raise ValueError('Can only specify at most one of buckets and labels.')
         if labels is None:
           labels = []
-        self._labelnames = labels
+        self._labelnames = tuple(labels)
         if buckets is not None:
           self.add_metric([], buckets, sum_value)
 
 
@@ -389,6 +389,16 @@ def test_bad_constructors(self):
         self.assertRaises(ValueError, HistogramMetricFamily, 'h', 'help', buckets={}, sum_value=1, labels=['a'])
         self.assertRaises(KeyError, HistogramMetricFamily, 'h', 'help', buckets={}, sum_value=1)
 
+    def test_labelnames(self):
+        cmf = CounterMetricFamily('c', 'help', labels=iter(['a']))
+        self.assertEqual(('a',), cmf._labelnames)
+        gmf = GaugeMetricFamily('g', 'help', labels=iter(['a']))
+        self.assertEqual(('a',), gmf._labelnames)
+        smf = SummaryMetricFamily('s', 'help', labels=iter(['a']))
+        self.assertEqual(('a',), smf._labelnames)
+        hmf = HistogramMetricFamily('h', 'help', labels=iter(['a']))
+        self.assertEqual(('a',), hmf._labelnames)
+
 
 class TestCollectorRegistry(unittest.TestCase):
     def test_duplicate_metrics_raises(self):