diff --git a/brainbox/task/closed_loop.py b/brainbox/task/closed_loop.py
index 96810f6ff..d32102177 100644
--- a/brainbox/task/closed_loop.py
+++ b/brainbox/task/closed_loop.py
@@ -388,7 +388,7 @@ def generate_pseudo_stimuli(n_trials, contrast_set=[0, 0.06, 0.12, 0.25, 1], fir
     return p_left, contrast_left, contrast_right
 
 
-def generate_pseudo_session(trials, generate_choices=True):
+def generate_pseudo_session(trials, generate_choices=True, contrast_distribution='biased'):
     """
     Generate a complete pseudo session with biased blocks, all stimulus contrasts, choices and
     rewards and omissions. Biased blocks and stimulus contrasts are generated using the same
@@ -426,7 +426,7 @@ def generate_pseudo_session(trials, generate_choices=True):
 
         # Draw position and contrast for this trial
         position = _draw_position([-1, 1], pseudo_trials['probabilityLeft'][i])
-        contrast = _draw_contrast(contrast_set, 'uniform')
+        contrast = _draw_contrast(contrast_set, prob_type=contrast_distribution, idx=np.where(contrast_set == 0)[0][0])
         signed_stim = contrast * np.sign(position)
 
         if generate_choices:
diff --git a/brainbox/tests/test_task.py b/brainbox/tests/test_task.py
index 5e7e85684..402b57c82 100755
--- a/brainbox/tests/test_task.py
+++ b/brainbox/tests/test_task.py
@@ -105,8 +105,19 @@ def test_generate_pseudo_stimuli(self):
 
     def test_generate_pseudo_session(self):
         test_trials = self.test_trials
-        pseudo_trials = task.generate_pseudo_session(test_trials)
-        self.assertTrue(pseudo_trials.shape[0] == test_trials.shape[0])
+        c = np.zeros(9)
+        np.random.seed(456)
+        for m in np.arange(10):
+            pseudo_trials = task.generate_pseudo_session(test_trials, generate_choices=False, contrast_distribution='biased')
+            c += pseudo_trials.groupby("signed_contrast")['signed_contrast'].count().values / pseudo_trials.shape[0]
+        self.assertTrue(np.all(np.round(c * 2) / 2 == 1))
+        c = np.zeros(9)
+        np.random.seed(456)
+        for m in np.arange(10):
+            pseudo_trials = task.generate_pseudo_session(test_trials, generate_choices=False,
+                                                         contrast_distribution='uniform')
+            c += pseudo_trials.groupby("signed_contrast")['signed_contrast'].count().values / pseudo_trials.shape[0]
+        self.assertTrue(np.all(np.round(c * 2) / 2 == np.array([1., 1., 1., 1., 2., 1., 1., 1., 1.])))
 
     def test_get_impostor_target(self):
         # labels between 3 and 14
diff --git a/ibllib/__init__.py b/ibllib/__init__.py
index 05e6e1a90..f890e2d0e 100644
--- a/ibllib/__init__.py
+++ b/ibllib/__init__.py
@@ -1,4 +1,4 @@
-__version__ = "2.13.4"
+__version__ = "2.13.5"
 import warnings
 
 from ibllib.misc import logger_config
diff --git a/release_notes.md b/release_notes.md
index 93b957a32..a6d4b8fdc 100644
--- a/release_notes.md
+++ b/release_notes.md
@@ -1,4 +1,7 @@
 ## Release Notes 2.13
+## Release Notes 2.13.4 2022-07-27
+- Hotfix: pseudo session biased generation contrast distribution
+
 ## Release Notes 2.13.4 2022-07-22
 - Hotfix: Density displays had unexisting colormaps in snapshots QC tasks
 - Generate extra training plots based on psychometric curves