diff --git a/rmgpy/chemkin.pyx b/rmgpy/chemkin.pyx
index 36c53b71bf..0c9f3bd434 100644
--- a/rmgpy/chemkin.pyx
+++ b/rmgpy/chemkin.pyx
@@ -2303,7 +2303,7 @@ def write_elements_section(f):
     s = 'ELEMENTS\n'
 
     # map of isotope elements with chemkin-compatible element representation:
-    elements = ('H', ('H', 2), ('H', 3), 'C', ('C', 13), 'O', ('O', 18), 'N', 'Ne', 'Ar', 'He', 'Si', 'S', 'Cl')
+    elements = ('H', ('H', 2), ('H', 3), 'C', ('C', 13), 'O', ('O', 18), 'N', 'Ne', 'Ar', 'He', 'Si', 'S', 'Cl', 'I')
     for el in elements:
         if isinstance(el, tuple):
             symbol, isotope = el