diff --git a/sparc/sparc_parsers/ion.py b/sparc/sparc_parsers/ion.py
index 280eefb3..cf8708a4 100644
--- a/sparc/sparc_parsers/ion.py
+++ b/sparc/sparc_parsers/ion.py
@@ -129,7 +129,7 @@ def _write_ion(
         ]:
             val = block.get(key, None)
             # print(key, val)
-            if (key not in ["RELAX", "COORD", "COORD_FRAC"]) and (val is None):
+            if (key not in ["RELAX", "COORD", "COORD_FRAC", "SPIN"]) and (val is None):
                 raise ValueError(f"Key {key} is not provided! Abort writing ion file")
             # TODO: change the API version
             if val is None: