diff --git a/Doc/libthread.tex b/Doc/libthread.tex
index fcee360..911c145 100644
--- a/Doc/libthread.tex
+++ b/Doc/libthread.tex
@@ -13,7 +13,7 @@
 \index{semaphores, binary}
 
 The module is optional.  It is supported on Windows NT and '95, SGI
-IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
+IRIX, Solaris 2.x, as well as on systems that have a \POSIX{} thread
 (a.k.a. ``pthread'') implementation.
 \index{pthreads}
 \indexii{threads}{posix}