diff --git a/csst_ifs_sim/csst_ifs_sim.py b/csst_ifs_sim/csst_ifs_sim.py
index 901359ab983824c494a5eaf8edf0276ea0bf48b7..6edb19675175c1a102d28b1a0c423a81d888a0b8 100644
--- a/csst_ifs_sim/csst_ifs_sim.py
+++ b/csst_ifs_sim/csst_ifs_sim.py
@@ -5061,7 +5061,7 @@ if __name__ == "__main__":
     applyhole = 'no'
 
     if CSST_unittest:
-        dir_path = os.path.join(os.environ['UNIT_TEST_DATA_ROOT'], 'ifs_sim')
+        dir_path = os.path.join(os.environ['UNIT_TEST_DATA_ROOT'], 'ifs_sim/')
     else:
         dir_path = '../'