diff --git a/doc/manual/env-common.xml b/doc/manual/env-common.xml
index 91a3e9e32..3d0b35f3e 100644
--- a/doc/manual/env-common.xml
+++ b/doc/manual/env-common.xml
@@ -9,8 +9,8 @@
 
 <variablelist xml:id="env-common">
 
-  
-<varlistentry><term><envar>NIX_PATH</envar></term>
+
+<varlistentry xml:id="env-NIX_PATH"><term><envar>NIX_PATH</envar></term>
 
   <listitem>
 
@@ -26,7 +26,7 @@
     <filename>/home/eelco/Dev</filename> and
     <filename>/etc/nixos</filename>, in that order.  It is also
     possible to match paths against a prefix.  For example, the value
-    
+
     <screen>
 nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos</screen>
 
@@ -37,12 +37,12 @@ nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos</screen>
     <filename>/etc/nixos/nixpkgs/<replaceable>path</replaceable></filename>.
     </para>
 
-    <para>The search path can be extended using the
-    <option>-I</option> option, which takes precedence over
+    <para>The search path can be extended using the <option
+    linkend="opt-I">-I</option> option, which takes precedence over
     <envar>NIX_PATH</envar>.</para></listitem>
 
 </varlistentry>
-    
+
 
 <varlistentry><term><envar>NIX_IGNORE_SYMLINK_STORE</envar></term>
 
@@ -65,7 +65,7 @@ nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos</screen>
   you’re better off using <literal>bind</literal> mount points, e.g.,
 
   <screen>
-$ mkdir /nix   
+$ mkdir /nix
 $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
   Consult the <citerefentry><refentrytitle>mount</refentrytitle>
@@ -80,7 +80,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
   <listitem><para>Overrides the location of the Nix store (default
   <filename><replaceable>prefix</replaceable>/store</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -89,7 +89,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
   <listitem><para>Overrides the location of the Nix static data
   directory (default
   <filename><replaceable>prefix</replaceable>/share</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -97,7 +97,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
   <listitem><para>Overrides the location of the Nix log directory
   (default <filename><replaceable>prefix</replaceable>/log/nix</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -105,7 +105,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
   <listitem><para>Overrides the location of the Nix state directory
   (default <filename><replaceable>prefix</replaceable>/var/nix</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -114,7 +114,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
   <listitem><para>Overrides the location of the Nix database (default
   <filename><replaceable>$NIX_STATE_DIR</replaceable>/db</filename>, i.e.,
   <filename><replaceable>prefix</replaceable>/var/nix/db</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -123,7 +123,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
   <listitem><para>Overrides the location of the Nix configuration
   directory (default
   <filename><replaceable>prefix</replaceable>/etc/nix</filename>).</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -133,7 +133,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
   files.  In particular, this includes temporary build directories;
   these can take up substantial amounts of disk space.  The default is
   <filename>/tmp</filename>.</para></listitem>
-  
+
 </varlistentry>
 
 
@@ -231,7 +231,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
       store derivation itself).</para></listitem>
 
     </varlistentry>
-  
+
     <varlistentry><term><filename>outputs</filename></term>
 
       <listitem><para>The set of store paths that are outputs of the
@@ -280,7 +280,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
 </varlistentry>
 
-    
+
 <varlistentry xml:id="envar-other-stores"><term><envar>NIX_OTHER_STORES</envar></term>
 
   <listitem><para>This variable contains the paths of remote Nix
@@ -331,7 +331,7 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
 
 </varlistentry>
 
-    
+
 </variablelist>
 
 
diff --git a/doc/manual/nix-instantiate.xml b/doc/manual/nix-instantiate.xml
index 936f154dd..6a4348f00 100644
--- a/doc/manual/nix-instantiate.xml
+++ b/doc/manual/nix-instantiate.xml
@@ -103,9 +103,10 @@ input.</para>
   <varlistentry><term><option>--find-file</option></term>
 
     <listitem><para>Look up the given files in Nix’s search path (as
-    specified by the <envar>NIX_PATH</envar> environment variable).
-    If found, print the corresponding absolute paths on standard
-    output.  For instance, if <envar>NIX_PATH</envar> is
+    specified by the <envar linkend="env-NIX_PATH">NIX_PATH</envar>
+    environment variable).  If found, print the corresponding absolute
+    paths on standard output.  For instance, if
+    <envar>NIX_PATH</envar> is
     <literal>nixpkgs=/home/alice/nixpkgs</literal>, then
     <literal>nix-instantiate --find-file nixpkgs/default.nix</literal>
     will print
diff --git a/doc/manual/opt-common.xml b/doc/manual/opt-common.xml
index f8584f4d6..7cef96b1b 100644
--- a/doc/manual/opt-common.xml
+++ b/doc/manual/opt-common.xml
@@ -351,13 +351,14 @@
 </varlistentry>
 
 
-<varlistentry><term><option>-I</option> <replaceable>path</replaceable></term>
+<varlistentry xml:id="opt-I"><term><option>-I</option> <replaceable>path</replaceable></term>
 
   <listitem><para>Add a path to the Nix expression search path.  This
-  option may be given multiple times.  See the <envar>NIX_PATH</envar>
-  environment variable for information on the semantics of the Nix
-  search path.  Paths added through <option>-I</option> take
-  precedence over <envar>NIX_PATH</envar>.</para></listitem>
+  option may be given multiple times.  See the <envar
+  linkend="env-NIX_PATH">NIX_PATH</envar> environment variable for
+  information on the semantics of the Nix search path.  Paths added
+  through <option>-I</option> take precedence over
+  <envar>NIX_PATH</envar>.</para></listitem>
 
 </varlistentry>