diff --git a/chainerrl/replay_buffers/prioritized.py b/chainerrl/replay_buffers/prioritized.py
index 3519fe0c8..c77fd6f7f 100644
--- a/chainerrl/replay_buffers/prioritized.py
+++ b/chainerrl/replay_buffers/prioritized.py
@@ -65,7 +65,7 @@ def _clip_error(error):
     def weights_from_probabilities(self, probabilities, min_probability):
         if self.normalize_by_max == 'batch':
             # discard global min and compute batch min
-            min_probability = np.min(min_probability)
+            min_probability = np.min(probabilities)
         if self.normalize_by_max:
             weights = [(p / min_probability) ** -self.beta
                        for p in probabilities]
diff --git a/tests/test_replay_buffer.py b/tests/test_replay_buffer.py
index 555d1165e..ea4cf9004 100644
--- a/tests/test_replay_buffer.py
+++ b/tests/test_replay_buffer.py
@@ -337,6 +337,52 @@ def test_append_and_sample(self):
         s4 = rbuf.sample(2)
         self.assertAlmostEqual(s4[0][0]['weight'], s4[1][0]['weight'])
 
+    def test_normalize_by_max(self):
+
+        rbuf = replay_buffer.PrioritizedReplayBuffer(
+            self.capacity,
+            normalize_by_max=self.normalize_by_max,
+            error_max=1000,
+            num_steps=self.num_steps,
+        )
+
+        # Add 100 transitions
+        for i in range(100):
+            trans = dict(state=i, action=1, reward=2, next_state=i + 1,
+                         next_action=1, is_state_terminal=False)
+            rbuf.append(**trans)
+        assert len(rbuf) == 100
+
+        def set_errors_based_on_state(rbuf, samples):
+            # Use the value of 'state' as an error, so that state 0 will have
+            # the smallest error, thus the largest weight
+            errors = [s[0]['state'] for s in samples]
+            rbuf.update_errors(errors)
+
+        # Assign different errors to all the transitions first
+        samples = rbuf.sample(100)
+        set_errors_based_on_state(rbuf, samples)
+
+        # Repeatedly check how weights are normalized
+        for i in range(100):
+            samples = rbuf.sample(i + 1)
+            # All the weights must be unique
+            self.assertEqual(
+                len(set(s[0]['weight'] for s in samples)), len(samples))
+            # Now check the maximum weight in a minibatch
+            max_w = max([s[0]['weight'] for s in samples])
+            if self.normalize_by_max == 'batch':
+                # Maximum weight in a minibatch must be 1
+                self.assertAlmostEqual(max_w, 1)
+            elif self.normalize_by_max == 'memory':
+                # Maximum weight in a minibatch must be less than 1 unless
+                # the minibatch contains the transition of least error.
+                if any(s[0]['state'] == 0 for s in samples):
+                    self.assertAlmostEqual(max_w, 1)
+                else:
+                    self.assertLess(max_w, 1)
+            set_errors_based_on_state(rbuf, samples)
+
     def test_capacity(self):
         capacity = self.capacity
         if capacity is None: