diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index 45e29214fb1a49b8231935f7322f1665be7bae3b..eb6d11fa2b937620fb9d75aac0812513265b6d5e 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -12,6 +12,7 @@ from ohmpi.utils import update_dict
 from ohmpi.config import HARDWARE_CONFIG
 from threading import Thread, Event, Barrier
 
+plt.switch_backend('agg') # for multi-threading...
 # Define the default controller, a distinct controller could be defined for each tx, rx or mux board
 # when using a distinct controller, the specific controller definition must be included in the component configuration
 ctl_module = importlib.import_module(f'ohmpi.hardware_components.{HARDWARE_CONFIG["ctl"]["model"]}')
diff --git a/ohmpi/plots.py b/ohmpi/plots.py
index 0e45d3caf398ad3ea115e332d2e6f85774491141..cd735ff575c056181e0e4518cbbe59dbd37ced4f 100644
--- a/ohmpi/plots.py
+++ b/ohmpi/plots.py
@@ -2,6 +2,7 @@ import matplotlib.pyplot as plt
 import numpy as np
 from ohmpi.utils import parse_log
 import matplotlib
+plt.switch_backend('agg') # for multi-threading...
 
 
 def plot_exec_log(exec_log,names=None,last_session=True):  # TODO: select session id instead of last session (if -1 : last)