diff --git a/reference/strings/functions/htmlspecialchars.xml b/reference/strings/functions/htmlspecialchars.xml
index 3eeab451c8..cf97aeb83f 100644
--- a/reference/strings/functions/htmlspecialchars.xml
+++ b/reference/strings/functions/htmlspecialchars.xml
@@ -106,9 +106,10 @@
        <literal>ISO-8859-1</literal>, <literal>ISO-8859-15</literal>,
        <literal>UTF-8</literal>, <literal>cp866</literal>,
        <literal>cp1251</literal>, <literal>cp1252</literal>, and
-       <literal>KOI8-R</literal> are effectively equivalent, as the
-       characters affected by <function>htmlspecialchars</function>
-       occupy the same positions in all of these charsets.
+       <literal>KOI8-R</literal> are effectively equivalent, provided the
+       <parameter>string</parameter> itself is valid for the character set, as
+       the characters affected by <function>htmlspecialchars</function> occupy
+       the same positions in all of these charsets.
       </para>
       &reference.strings.charsets;
      </listitem>
@@ -131,6 +132,12 @@
   <para>
    The converted <type>string</type>.
   </para>
+  <para>
+   If the input <parameter>string</parameter> contains an invalid code unit
+   sequence within the given <parameter>charset</parameter> and the
+   <constant>ENT_IGNORE</constant> flag is not set, then
+   <function>htmlspecialchars</function> will return an empty string.
+  </para>
  </refsect1>
 
  <refsect1 role="changelog">