diff --git a/prometheus_client/metrics.py b/prometheus_client/metrics.py
index e3fe5323..a48e8199 100644
--- a/prometheus_client/metrics.py
+++ b/prometheus_client/metrics.py
@@ -639,10 +639,10 @@ def __init__(self,
 
     def _prepare_buckets(self, source_buckets: Sequence[Union[float, str]]) -> None:
         buckets = [float(b) for b in source_buckets]
-        if buckets != sorted(buckets):
+        if any(not lower < upper for lower, upper in zip(buckets, buckets[1:])):
             # This is probably an error on the part of the user,
             # so raise rather than sorting for them.
-            raise ValueError('Buckets not in sorted order')
+            raise ValueError('Buckets not in strictly increasing order')
         if buckets and buckets[-1] != INF:
             buckets.append(INF)
         if len(buckets) < 2:
diff --git a/tests/test_core.py b/tests/test_core.py
index 3aa19c24..3a97c3ea 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -458,6 +458,10 @@ def test_setting_buckets(self):
         self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[])
         self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[float("inf")])
         self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[3, 1])
+        self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[1, 1, 2])
+        self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[1, '1.0'])
+        self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[1, float("inf"), float("inf")])
+        self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[1, float("nan")])
 
     def test_labels(self):
         self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, labelnames=['le'])