diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 4001447..0fb8f10 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -702,9 +702,12 @@
 Availability: Macintosh, \UNIX{}, Windows.
 \end{funcdesc}
 
-\begin{funcdesc}{utime}{path, (atime, mtime)}
-Set the access and modified time of the file to the given values.
-(The second argument is a tuple of two items.)
+\begin{funcdesc}{utime}{path, times}
+Set the access and modified times of the file specified by \var{path}.
+If \var{times} is \code{None}, then the file's access and modified
+times are set to the current time.  Otherwise, \var{times} must be a
+2-tuple of numbers, of the form \var{(atime, mtime)} which is used to
+set the access and modified times, respectively.
 Availability: Macintosh, \UNIX{}, Windows.
 \end{funcdesc}