diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 16f3690..1c3a584 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -315,6 +315,12 @@
 objects should be opened in binary or text mode.  The default value
 for \var{mode} is \code{'t'}.
 
+These methods do not make it possible to retrieve the return code from
+the child processes.  The only way to control the input and output
+streams and also retrieve the return codes is to use the
+\class{Popen3} and \class{Popen4} classes from the \refmodule{popen2}
+module; these are only available on \UNIX.
+
 \begin{funcdesc}{popen2}{cmd\optional{, mode\optional{, bufsize}}}
 Executes \var{cmd} as a sub-process.  Returns the file objects
 \code{(\var{child_stdin}, \var{child_stdout})}.
diff --git a/Doc/lib/libpopen2.tex b/Doc/lib/libpopen2.tex
index add0af1..8cdf0f5 100644
--- a/Doc/lib/libpopen2.tex
+++ b/Doc/lib/libpopen2.tex
@@ -24,6 +24,13 @@
 in binary or text mode.  The default value for \var{mode} is
 \code{'t'}.
 
+The only way to retrieve the return codes for the child processes is
+by using the \method{poll()} or \method{wait()} methods on the
+\class{Popen3} and \class{Popen4} classes; these are only available on
+\UNIX.  This information is not available when using the
+\function{popen2()}, \function{popen3()}, and \function{popen4()}
+functions, or the equivalent functions in the \refmodule{os} module.
+
 \begin{funcdesc}{popen2}{cmd\optional{, bufsize\optional{, mode}}}
 Executes \var{cmd} as a sub-process.  Returns the file objects
 \code{(\var{child_stdout}, \var{child_stdin})}.