diff --git a/Doc/lib/libthread.tex b/Doc/lib/libthread.tex
index d2a34a1..052867f 100644
--- a/Doc/lib/libthread.tex
+++ b/Doc/lib/libthread.tex
@@ -45,7 +45,8 @@
 
 \begin{funcdesc}{interrupt_main}{}
 Raise a KeyboardInterrupt in the main thread.  A subthread can use this
-function to to interrupt the main thread.
+function to interrupt the main thread.
+\versionadded{2.3}
 \end{funcdesc}
 
 \begin{funcdesc}{exit}{}