diff --git a/reference/exif/functions/exif-thumbnail.xml b/reference/exif/functions/exif-thumbnail.xml
index 3b8119096e..d7cfa151c0 100644
--- a/reference/exif/functions/exif-thumbnail.xml
+++ b/reference/exif/functions/exif-thumbnail.xml
@@ -11,9 +11,9 @@
   <methodsynopsis>
    <type class="union"><type>string</type><type>false</type></type><methodname>exif_thumbnail</methodname>
    <methodparam><type class="union"><type>resource</type><type>string</type></type><parameter>file</parameter></methodparam>
-   <methodparam choice="opt"><type>int</type><parameter role="reference">width</parameter></methodparam>
-   <methodparam choice="opt"><type>int</type><parameter role="reference">height</parameter></methodparam>
-   <methodparam choice="opt"><type>int</type><parameter role="reference">image_type</parameter></methodparam>
+   <methodparam choice="opt"><type>int</type><parameter role="reference">width</parameter><initializer>&null;</initializer></methodparam>
+   <methodparam choice="opt"><type>int</type><parameter role="reference">height</parameter><initializer>&null;</initializer></methodparam>
+   <methodparam choice="opt"><type>int</type><parameter role="reference">image_type</parameter><initializer>&null;</initializer></methodparam>
   </methodsynopsis>
   <para>
    <function>exif_thumbnail</function> reads the embedded thumbnail of an image.