diff --git a/src/PilatusXM.py b/src/PilatusXM.py
index 869051759c7ebf28dc4c9c7022ef2823f6ed8ee1..0f0dc78176d946750b97fb8a87a19b961099fe13 100755
--- a/src/PilatusXM.py
+++ b/src/PilatusXM.py
@@ -217,7 +217,7 @@ class PilatusXM (PyTango.LatestDeviceImpl):
                 if elapsed_time > self.total_exp_time:
                     self.set_state(PyTango.DevState.ON)
                     self.set_status("The device is in ON state. Ready")
-                    filenum = self.attr_FileStartNum_read + self.attr_NbFrames_read
+                    filenum = self.attr_FileStartNum_read + self.attr_NbFrames_read - 1
                     fullname = "%s%05d%s" % (self.attr_FilePrefix_read,filenum,self.attr_FilePostfix_read)
                     self.attr_LastImagePath_read = os.path.join(self.attr_FileDir_read,fullname)
                     self.attr_LastImageTaken_read = os.path.join(self.attr_FileDir_read,fullname)