diff --git a/pysqm/read.py b/pysqm/read.py
index 71cba3090be359a44f58163e79608123576a95ad..716319250d92271ae4d10b773c92fb2c4a14455d 100644
--- a/pysqm/read.py
+++ b/pysqm/read.py
@@ -191,7 +191,7 @@ class device(observatory):
 
         self.monthly_datafile = \
          config.monthly_data_directory+"/"+yearmonth+"_"+\
-         config._device_shorttype+"_"+config._observatory_name+"_"+".dat"
+         config._device_shorttype+"_"+config._observatory_name+".dat"
         self.daily_datafile = \
          config.daily_data_directory+"/"+yearmonth+"/"+\
          yearmonthday+"_"+config._device_shorttype+"_"+config._observatory_name+'.dat'