diff --git a/samples/gibbs_ensemble/gibbs_ensemble.py b/samples/gibbs_ensemble/gibbs_ensemble.py
index dda9eb6d06f..6eb26962ef1 100644
--- a/samples/gibbs_ensemble/gibbs_ensemble.py
+++ b/samples/gibbs_ensemble/gibbs_ensemble.py
@@ -80,7 +80,8 @@ def send_info(self):
 
     def move_particle(self, DX_MAX):
         """ Move random particle inside the box """
-        self.old_particle = np.random.choice(self.system.part)
+        random_particle_id = np.random.choice(self.system.part[:].id)
+        self.old_particle = self.system.part[random_particle_id]
         self.old_pos = self.old_particle.pos
         self.old_particle.pos = self.old_pos + \
             (0.5 - np.random.random(size=3)) * DX_MAX
@@ -104,7 +105,8 @@ def revert_add_particle(self):
 
     def remove_particle(self):
         """ Remove a random particle """
-        self.old_particle = np.random.choice(self.system.part).to_dict()
+        random_particle_id = np.random.choice(self.system.part[:].id)
+        self.old_particle = self.system.part[random_particle_id].to_dict()
         self.system.part[self.old_particle["id"]].remove()
         self.send_energy()
 
diff --git a/samples/gibbs_ensemble/run_sim.py b/samples/gibbs_ensemble/run_sim.py
index b3b8e887132..0de54d692f9 100644
--- a/samples/gibbs_ensemble/run_sim.py
+++ b/samples/gibbs_ensemble/run_sim.py
@@ -222,7 +222,7 @@ def validate_info(boxes):
         np.testing.assert_equal(
             box.num_part,
             msg[2],
-            err_msg="Server side box length (actual) differs from client side (desired)")
+            err_msg="Server side num part (actual) differs from client side (desired)")
         logging.debug(
             "Validation correct. Values of {}:\nBox length:\t{}\nNum Part:\t{}.".format(
                 box.box_name, box.box_length, box.num_part))