add versionadded for getcheckinterval
diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index ea4aafa..8f8b5cc 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -200,6 +200,7 @@
 \begin{funcdesc}{getcheckinterval}{}
   Return the interpreter's ``check interval'';
   see \function{setcheckinterval()}.
+  \versionadded{2.3}
 \end{funcdesc}
 
 \begin{funcdesc}{getdefaultencoding}{}