Be consistent in presenting the signatures.
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 5819f80..7e677c9 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -101,7 +101,7 @@
 \end{datadesc}
 
 \begin{funcdescni}{chdir}{path}
-\funclineni{fchdir}{}
+\funclineni{fchdir}{fd}
 \funclineni{getcwd}{}
 These functions are described in ``Files and Directories'' (section
 \ref{os-file-dir}).