diff --git a/reference/strings/functions/strlen.xml b/reference/strings/functions/strlen.xml
index 8884cae854..00390e5538 100644
--- a/reference/strings/functions/strlen.xml
+++ b/reference/strings/functions/strlen.xml
@@ -38,6 +38,7 @@
   <para>
    The length of the <parameter>string</parameter> on success, 
    and <literal>0</literal> if the <parameter>string</parameter> is empty.
+   Will return &null; on failure.
   </para>
  </refsect1>
 
@@ -55,6 +56,7 @@
      <row>
       <entry>5.3.0</entry>
       <entry>
+       Returns &null; on failure.
        Prior versions treated arrays as the string <literal>Array</literal>, thus returning
        a string length of <literal>5</literal> and emitting an <constant>E_NOTICE</constant> level error.
       </entry>