diff --git a/sotodlib/core/axisman_io.py b/sotodlib/core/axisman_io.py
index 94135d7a3..ce5c5a177 100644
--- a/sotodlib/core/axisman_io.py
+++ b/sotodlib/core/axisman_io.py
@@ -283,7 +283,7 @@ def _save_axisman(axisman, dest, group=None, overwrite=False, compression=None,
             print(f'Unhandled {item["name"]}->{item["encoding"]}')
 
     if len(scalars):
-        dest.attrs['_scalars'] = json.dumps(scalars)
+        dest.attrs['_scalars'] = json.dumps(_safe_scalars(scalars))
 
     if len(units):
         dest.attrs['_units'] = json.dumps(units)