diff --git a/doc/sphinx/cti/species.rst b/doc/sphinx/cti/species.rst
index c6a1c7a8a..20de419b9 100644
--- a/doc/sphinx/cti/species.rst
+++ b/doc/sphinx/cti/species.rst
@@ -19,7 +19,7 @@ definitions.  An explicit element entry is needed only if an isotope not in
 
     element(symbol='C-13',
             atomic_mass=13.003354826)
-    element("O-!8", 17.9991603)
+    element("O-18", 17.9991603)
 
 Species
 =======