fix use of undefined markup
diff --git a/Doc/api/concrete.tex b/Doc/api/concrete.tex
index 7ad6e91..bf8d438 100644
--- a/Doc/api/concrete.tex
+++ b/Doc/api/concrete.tex
@@ -98,7 +98,7 @@
 \end{cvardesc}
 
 \begin{csimplemacrodesc}{Py_RETURN_NONE}
-  Properly handles returning \cvar{Py_None} from within a C function.
+  Properly handles returning \cdata{Py_None} from within a C function.
 \end{csimplemacrodesc}