diff --git a/ObservationSim/sim_steps/readout_output.py b/ObservationSim/sim_steps/readout_output.py
index 1702a01914c6ba953cee77c516ab43a909858623..ab75f07648ee402f2997b6ea04a84f8b4566d8e1 100644
--- a/ObservationSim/sim_steps/readout_output.py
+++ b/ObservationSim/sim_steps/readout_output.py
@@ -16,7 +16,7 @@ def add_prescan_overscan(self, chip, filt, tel, pointing, catalog, obs_param):
     if obs_param["add_dark"] == True:
         ny = int(chip.npix_y/2)
         base_dark = (ny-1)*(chip.readout_time/ny)*chip.dark_noise
-        chip.img.array[(chip.prescan_y+ny):-(chip.prescan_y+ny),:] = bese_dark
+        chip.img.array[(chip.prescan_y+ny):-(chip.prescan_y+ny),:] = base_dark
     return chip, filt, tel, pointing
 
 def add_readout_noise(self, chip, filt, tel, pointing, catalog, obs_param):