diff --git a/tests/test_ifs_sim.py b/tests/test_ifs_sim.py
index 461a70194bb999702c96d7dc08b9a6256ac4428f..b0e251c43c43bc8995c311985bb078b938402cfa 100644
--- a/tests/test_ifs_sim.py
+++ b/tests/test_ifs_sim.py
@@ -37,7 +37,7 @@ class TestDemoFunction(unittest.TestCase):
         
         d=1
         
-        subprocess.run('csst_ifs_sim', dir_path)
+        subprocess.run(['csst_ifs_sim', dir_path])
         
         #csst_ifs_sim dir_path