diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index 27786fead1287b41490f5a3208db36a5c061ce7b..aa9f3cafd5775f17ab4de1ac273a3f73c3c68328 100755
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -534,7 +534,7 @@ class Instrument:
                 # Switch between various fplan file standards
                 if version in SpecifierSet('== 1.1.*', True):
                     logger.debug("Interpolating locking beatnote frequencies with piecewise linear functions")
-                    times = self.t0 + np.arange(fplanf.attrs['size']) * fplanf.attrs['dt']
+                    times = self.orbits_t0 + np.arange(fplanf.attrs['size']) * fplanf.attrs['dt']
                     interpolate = lambda x: InterpolatedUnivariateSpline(times, x, k=1, ext='raise')(self.physics_t)
                     lock_beatnotes = {}
                     # Go through all MOSAs and pick locking beatnotes
@@ -571,6 +571,7 @@ class Instrument:
         if orbits == 'static':
             logger.info("Using default set of static proper pseudo-ranges")
             self.orbit_file = None
+            self.orbits_t0 = self.t0
             self.pprs = ForEachMOSA({
                 # Default PPRs based on first samples of Keplerian orbits (v2.0.dev)
                 '12': 8.33242295, '23': 8.30282196, '31': 8.33242298,
@@ -599,6 +600,7 @@ class Instrument:
         else:
             logger.info("Using user-provided proper pseudo-ranges and derivatives")
             self.orbit_file = None
+            self.orbits_t0 = self.t0
             self.pprs = ForEachMOSA(orbits)
             self.d_pprs = self.pprs.transformed(lambda _, x:
                 0 if np.isscalar(x) else np.gradient(x, self.physics_dt)
@@ -641,6 +643,13 @@ class Instrument:
             raise ValueError(f"invalid orbit dataset '{self.orbit_dataset}'")
 
         try:
+            logger.debug("Reading orbit's t0")
+            if self.orbit_dataset == 'tcb/ltt':
+                self.orbits_t0 = orbitf['tcb']['t'][0]
+            elif self.orbit_dataset == 'tps/ppr':
+                self.orbits_t0 = orbitf['tps']['tau'][0]
+            else:
+                raise ValueError(f"invalid orbit dataset '{self.orbit_dataset}'")
             logger.debug("Interpolating proper pseudo-ranges")
             self.pprs = ForEachMOSA(lambda mosa: pprs(mosa)(self.physics_t))
             logger.debug("Interpolating proper pseudo-range derivatives")
@@ -663,6 +672,8 @@ class Instrument:
         # Interpolate necessary orbital quantities,
         # show a helpful error message if orbit file is too short
         try:
+            logger.debug("Reading orbit's t0")
+            self.orbits_t0 = orbitf.attrs['t0']
             logger.debug("Interpolating proper pseudo-ranges")
             dataset = orbitf['tcb/ltt'] if self.orbit_dataset == 'tcb/ltt' else orbitf['tps/ppr']
             self.pprs = ForEachMOSA(lambda mosa: interpolate(dataset[:, link_index[mosa]], self.physics_t))