diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 9159131de6b..cfb32f8b1c3 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -595,7 +595,7 @@ These can be bit-wise OR'd together.
 Availability: Macintosh, \UNIX, Windows.
 \end{datadesc}
 
-begin{datadesc}{O_DSYNC}
+\begin{datadesc}{O_DSYNC}
 \dataline{O_RSYNC}
 \dataline{O_SYNC}
 \dataline{O_NDELAY}