diff --git a/Doc/lib/libsubprocess.tex b/Doc/lib/libsubprocess.tex
index 01f64ae..77bd83e 100644
--- a/Doc/lib/libsubprocess.tex
+++ b/Doc/lib/libsubprocess.tex
@@ -239,7 +239,7 @@
 output=`dmesg | grep hda`
 ==>
 p1 = Popen(["dmesg"], stdout=PIPE)
-p2 = Popen(["grep", "hda"], stdin=p1.stdout)
+p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
 output = p2.communicate()[0]
 \end{verbatim}