diff --git a/nixos/lib/make-options-doc/options-to-docbook.xsl b/nixos/lib/make-options-doc/options-to-docbook.xsl
index 72ac89d4ff6..18d19fddaca 100644
--- a/nixos/lib/make-options-doc/options-to-docbook.xsl
+++ b/nixos/lib/make-options-doc/options-to-docbook.xsl
@@ -20,7 +20,7 @@
       <title>Configuration Options</title>
       <variablelist xml:id="configuration-variable-list">
         <xsl:for-each select="attrs">
-          <xsl:variable name="id" select="concat('opt-', str:replace(str:replace(str:replace(str:replace(attr[@name = 'name']/string/@value, '*', '_'), '&lt;', '_'), '>', '_'), '?', '_'))" />
+          <xsl:variable name="id" select="concat('opt-', str:replace(str:replace(str:replace(attr[@name = 'name']/string/@value, '*', '_'), '&lt;', '_'), '>', '_'))" />
           <varlistentry>
             <term xlink:href="#{$id}">
               <xsl:attribute name="xml:id"><xsl:value-of select="$id"/></xsl:attribute>