diff --git a/reference/strings/functions/rtrim.xml b/reference/strings/functions/rtrim.xml
index fc9a0b9297..712f68d457 100644
--- a/reference/strings/functions/rtrim.xml
+++ b/reference/strings/functions/rtrim.xml
@@ -49,7 +49,7 @@
     <listitem>
      <simpara>
       "\0" (<acronym>ASCII</acronym> <literal>0</literal>
-      (<literal>0x00</literal>)), the <literal>NUL</literal>-byte.
+      (<literal>0x00</literal>)), the <literal>NULL</literal>-byte.
      </simpara>
     </listitem>
     <listitem>