diff --git a/lya_2pt/forest_healpix_reader.py b/lya_2pt/forest_healpix_reader.py
index bed5a91..14c0933 100644
--- a/lya_2pt/forest_healpix_reader.py
+++ b/lya_2pt/forest_healpix_reader.py
@@ -112,6 +112,7 @@ def __init__(self, config, file, cosmo, auto_flag=False, need_distortion=False):
         rebin_factor = reader_config.getint("rebin")
         use_ivar = reader_config.getboolean("use-ivar")
         if rebin_factor > 1:
+            assert self.dwave is not None, "Rebinning does not work with old delta files"
             for tracer in self.tracers:
                 tracer.rebin(rebin_factor, self.dwave, absorption_line, use_ivar=use_ivar)
 
diff --git a/lya_2pt/read_io.py b/lya_2pt/read_io.py
index 5ba746d..add0257 100644
--- a/lya_2pt/read_io.py
+++ b/lya_2pt/read_io.py
@@ -97,7 +97,11 @@ def read_from_hdu(hdul, absorption_line, healpix_id, need_distortion=False, proj
     ReaderException if both LOGLAM and LAMBDA extensions are not
     in the HDU list
     """
-    dwave = hdul[1].read_header()['DELTA_LAMBDA']
+    header = hdul[1].read_header()
+    if 'DELTA_LAMBDA' in header:
+        dwave = ['DELTA_LAMBDA']
+    else:
+        dwave = None
 
     tracers = []
     wave_solution = None