diff --git a/DSSC1module.py b/DSSC1module.py
index 380e0c9e4bc0e3aff095a00691764f94d8832bdc..b053da1b2efd3e29135648eb3ef79480c092c4e9 100644
--- a/DSSC1module.py
+++ b/DSSC1module.py
@@ -106,7 +106,7 @@ class DSSC1module:
         except:
             self.delay_mm = 0*self.nrj
         self.t0 = t0
-        self.delay_ps = tb.positionToDelay(self.delay_mm, origin=self.t0)
+        self.delay_ps = tb.positionToDelay(self.delay_mm, origin=self.t0, invert=True)
                     
     def collect_dssc_module_file(self):
         """ Collect the raw DSSC module h5 files.