diff --git a/py/redrock/results.py b/py/redrock/results.py
index 2118e21..33ddb7a 100644
--- a/py/redrock/results.py
+++ b/py/redrock/results.py
@@ -47,8 +47,9 @@ def write_zscan(filename, zscan, zfit, clobber=False):
     zfit = zfit.copy()
 
     #- convert unicode to byte strings
-    zfit.replace_column('spectype', np.char.encode(zfit['spectype'], 'ascii'))
-    zfit.replace_column('subtype', np.char.encode(zfit['subtype'], 'ascii'))
+    for colname in ('spectype', 'subtype', 'fitmethod'):
+        if colname in zfit.columns:
+            zfit.replace_column(colname, np.char.encode(zfit[colname], 'ascii'))
 
     zbest = zfit[zfit['znum'] == 0]
     zbest.remove_column('znum')
diff --git a/py/redrock/test/test_io.py b/py/redrock/test/test_io.py
index 04c15ae..794b0dd 100644
--- a/py/redrock/test/test_io.py
+++ b/py/redrock/test/test_io.py
@@ -139,6 +139,8 @@ def test_zscan_io(self):
 
         zscan1, zfit1 = zfind(dtarg, [ dtemp ])
 
+        zfit1.remove_column('fitmethod')
+
         write_zscan(self.testfile, zscan1, zfit1)
         write_zscan(self.testfile, zscan1, zfit1, clobber=True)
         zscan2, zfit2 = read_zscan(self.testfile)