diff --git a/Doc/lib/libposix.tex b/Doc/lib/libposix.tex
index 467195fb7ac..454c652066f 100644
--- a/Doc/lib/libposix.tex
+++ b/Doc/lib/libposix.tex
@@ -292,6 +292,7 @@ object.
 \end{funcdesc}
 
 \begin{funcdesc}{putenv}{varname\, value}
+\index{environment variables!setting}
 Set the environment variable named \var{varname} to the string
 \var{value}.  Such changes to the environment affect subprocesses
 started with \function{os.system()}, \function{os.popen()} or
diff --git a/Doc/libposix.tex b/Doc/libposix.tex
index 467195fb7ac..454c652066f 100644
--- a/Doc/libposix.tex
+++ b/Doc/libposix.tex
@@ -292,6 +292,7 @@ object.
 \end{funcdesc}
 
 \begin{funcdesc}{putenv}{varname\, value}
+\index{environment variables!setting}
 Set the environment variable named \var{varname} to the string
 \var{value}.  Such changes to the environment affect subprocesses
 started with \function{os.system()}, \function{os.popen()} or