diff --git a/pyerrors/input/openQCD.py b/pyerrors/input/openQCD.py
index 73b95dd9..8b5fc91f 100644
--- a/pyerrors/input/openQCD.py
+++ b/pyerrors/input/openQCD.py
@@ -250,7 +250,7 @@ def _extract_flowed_energy_density(path, prefix, dtr_read, xmin, spatial_extent,
     dtr_read : int
         Determines how many trajectories should be skipped
         when reading the ms.dat files.
-        Corresponds to dtr_cnfg / dtr_ms (dncnfg / dnms) in the openQCD input file.
+        Corresponds to dtr_ms (dnms) in the openQCD input file.
     xmin : int
         First timeslice where the boundary
         effects have sufficiently decayed.
@@ -377,6 +377,8 @@ def _extract_flowed_energy_density(path, prefix, dtr_read, xmin, spatial_extent,
                             for current in range(0, len(item), tmax)])
 
         diffmeas = configlist[-1][-1] - configlist[-1][-2]
+        if not np.isclose(configlist[-1][0]/diffmeas, int(configlist[-1][0]/diffmeas), 1e-12):
+            raise ValueError("Spacing of the first configuration after thermalization is irregular.")
         configlist[-1] = [item // diffmeas for item in configlist[-1]]
         if kwargs.get('assume_thermalization', True) and configlist[-1][0] > 1:
             warnings.warn('Assume thermalization and that the first measurement belongs to the first config.')