diff --git a/reference/exec/functions/shell-exec.xml b/reference/exec/functions/shell-exec.xml
index f835c469a2..2e41113c19 100644
--- a/reference/exec/functions/shell-exec.xml
+++ b/reference/exec/functions/shell-exec.xml
@@ -38,7 +38,7 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   The output from the executed command or NULL if an error occurred.
+   The output from the executed command or &null; if an error occurred.
   </para>
  </refsect1>