diff --git a/docs/guide/examples.rst b/docs/guide/examples.rst
index 5935f50..818f282 100644
--- a/docs/guide/examples.rst
+++ b/docs/guide/examples.rst
@@ -209,8 +209,8 @@ These dictionaries are randomly initialized on the creation of the environment a
   model.learn(total_timesteps=100_000)
 
 
-Using Callback: Monitoring Training
------------------------------------
+Callbacks: Monitoring Training
+------------------------------
 
 .. note::
 
@@ -308,6 +308,49 @@ If your callback returns False, training is aborted early.
   plt.show()
 
 
+Callbacks: Evaluate Agent Performance
+-------------------------------------
+To periodically evaluate an agent's performance on a separate test environment, use ``EvalCallback``.
+You can control the evaluation frequency with ``eval_freq`` to monitor your agent's progress during training.
+
+.. code-block:: python
+
+  import os
+  import gymnasium as gym
+
+  from stable_baselines3 import SAC
+  from stable_baselines3.common.callbacks import EvalCallback
+  from stable-baselines3.common.env_util import make_vec_env
+
+  env_id = "Pendulum-v1"
+  n_training_envs = 1
+  n_eval_envs = 5
+
+  # Create log dir where evaluation results will be saved
+  eval_log_dir = "./eval_logs/"
+  os.makedirs(eval_log_dir, exist_ok=True)
+
+  # Initialize a vectorized training environment with default parameters
+  train_env = make_vec_env(env_id, n_env=n_training_envs, seed=0)
+
+  # Separate evaluation env, with different parameters passed via env_kwargs
+  # Eval environments can be vectorized to speed up evaluation.
+  eval_env = make_vec_env(env_id, n_envs=n_eval_envs, seed=0,
+                          env_kwargs={'g':0.7})
+
+  # Create callback that evaluates agent for 5 episodes every 500 training environment steps.
+  # When using multiple training environments, agent will be evaluated every
+  # eval_freq calls to train_env.step(), thus it will be evaluated every
+  # (eval_freq * n_envs) training steps. See EvalCallback doc for more information.
+  eval_callback = EvalCallback(eval_env, best_model_save_path=eval_log_dir,
+                                log_path=eval_log_dir, eval_freq=max(500 // n_training_envs, 1),
+                                n_eval_episodes=5, deterministic=True,
+                                render=False)
+
+  model = SAC("MlpPolicy", train_env)
+  model.learn(5000, callback=eval_callback)
+
+
 Atari Games
 -----------
 
diff --git a/docs/misc/changelog.rst b/docs/misc/changelog.rst
index a47118d..b23f764 100644
--- a/docs/misc/changelog.rst
+++ b/docs/misc/changelog.rst
@@ -3,7 +3,7 @@
 Changelog
 ==========
 
-Release 2.0.0a5 (WIP)
+Release 2.0.0a6 (WIP)
 --------------------------
 
 **Gymnasium support**
@@ -35,6 +35,8 @@ New Features:
 Bug Fixes:
 ^^^^^^^^^^
 - Fixed ``VecExtractDictObs`` does not handle terminal observation (@WeberSamuel)
+- Set NumPy version to ``>=1.20`` due to use of ``numpy.typing`` (@troiganto)
+- Fixed loading DQN changes ``target_update_interval`` (@tobirohrer)
 
 Deprecations:
 ^^^^^^^^^^^^^
@@ -59,6 +61,7 @@ Documentation:
 - Upgraded tutorials to Gymnasium API
 - Make it more explicit when using ``VecEnv`` vs Gym env
 - Added UAV_Navigation_DRL_AirSim to the project page (@heleidsn)
+- Added ``EvalCallback`` example (@sidney-tio)
 
 
 Release 1.8.0 (2023-04-07)
@@ -1332,4 +1335,4 @@ And all the contributors:
 @carlosluis @arjun-kg @tlpss
 @Melanol @qgallouedec @francescoluciano @jlp-ue @burakdmb @timothe-chaumont @honglu2875
 @anand-bala @hughperkins @sidney-tio @AlexPasqua @dominicgkerr @Akhilez @Rocamonde @tobirohrer @ZikangXiong
-@DavyMorgan @luizapozzobon @Bonifatius94 @theSquaredError @harveybellini @DavyMorgan @FieteO @jonasreiher @npit @WeberSamuel
+@DavyMorgan @luizapozzobon @Bonifatius94 @theSquaredError @harveybellini @DavyMorgan @FieteO @jonasreiher @npit @WeberSamuel @troiganto
diff --git a/setup.py b/setup.py
index a7a3fcc..d72e77d 100644
--- a/setup.py
+++ b/setup.py
@@ -103,7 +103,7 @@ setup(
     package_data={"stable_baselines3": ["py.typed", "version.txt"]},
     install_requires=[
         "gymnasium==0.28.1",
-        "numpy",
+        "numpy>=1.20",
         "torch>=1.11",
         'typing_extensions>=4.0,<5; python_version < "3.8.0"',
         # For saving models
diff --git a/stable_baselines3/dqn/dqn.py b/stable_baselines3/dqn/dqn.py
index b85a30f..bd3ad4b 100644
--- a/stable_baselines3/dqn/dqn.py
+++ b/stable_baselines3/dqn/dqn.py
@@ -151,8 +151,7 @@ class DQN(OffPolicyAlgorithm):
             self.exploration_final_eps,
             self.exploration_fraction,
         )
-        # Account for multiple environments
-        # each call to step() corresponds to n_envs transitions
+
         if self.n_envs > 1:
             if self.n_envs > self.target_update_interval:
                 warnings.warn(
@@ -162,8 +161,6 @@ class DQN(OffPolicyAlgorithm):
                     f"which corresponds to {self.n_envs} steps."
                 )
 
-            self.target_update_interval = max(self.target_update_interval // self.n_envs, 1)
-
     def _create_aliases(self) -> None:
         self.q_net = self.policy.q_net
         self.q_net_target = self.policy.q_net_target
@@ -174,7 +171,9 @@ class DQN(OffPolicyAlgorithm):
         This method is called in ``collect_rollouts()`` after each step in the environment.
         """
         self._n_calls += 1
-        if self._n_calls % self.target_update_interval == 0:
+        # Account for multiple environments
+        # each call to step() corresponds to n_envs transitions
+        if self._n_calls % max(self.target_update_interval // self.n_envs, 1) == 0:
             polyak_update(self.q_net.parameters(), self.q_net_target.parameters(), self.tau)
             # Copy running stats, see GH issue #996
             polyak_update(self.batch_norm_stats, self.batch_norm_stats_target, 1.0)
diff --git a/stable_baselines3/version.txt b/stable_baselines3/version.txt
index 0691e44..758664d 100644
--- a/stable_baselines3/version.txt
+++ b/stable_baselines3/version.txt
@@ -1 +1 @@
-2.0.0a5
+2.0.0a6
diff --git a/tests/test_save_load.py b/tests/test_save_load.py
index 2f227ad..9d0aa44 100644
--- a/tests/test_save_load.py
+++ b/tests/test_save_load.py
@@ -15,6 +15,7 @@ import torch as th
 
 from stable_baselines3 import A2C, DDPG, DQN, PPO, SAC, TD3
 from stable_baselines3.common.base_class import BaseAlgorithm
+from stable_baselines3.common.env_util import make_vec_env
 from stable_baselines3.common.envs import FakeImageEnv, IdentityEnv, IdentityEnvBox
 from stable_baselines3.common.save_util import load_from_pkl, open_path, save_to_pkl
 from stable_baselines3.common.utils import get_device
@@ -730,3 +731,14 @@ def test_load_invalid_object(tmp_path):
     with warnings.catch_warnings(record=True) as record:
         PPO.load(path, custom_objects=dict(learning_rate=lambda _: 1.0))
     assert len(record) == 0
+
+
+def test_dqn_target_update_interval(tmp_path):
+    # `target_update_interval` should not change when reloading the model. See GH Issue #1373.
+    env = make_vec_env(env_id="CartPole-v1", n_envs=2)
+    model = DQN("MlpPolicy", env, verbose=1, target_update_interval=100)
+    model.save(tmp_path / "dqn_cartpole")
+    del model
+    model = DQN.load(tmp_path / "dqn_cartpole")
+    os.remove(tmp_path / "dqn_cartpole.zip")
+    assert model.target_update_interval == 100