diff --git a/functions/image.xml b/functions/image.xml
index f7207e38ef..7d2273f224 100644
--- a/functions/image.xml
+++ b/functions/image.xml
@@ -85,6 +85,11 @@
     <literal>channel</literal> will be 3 for RGB pictures, and 4 for CMYK 
     pictures. <literal>bits</literal> is the number of bits for each color.
    </para>
+   <para>
+	If accessing the <parameter>filename</parameter> image is impossible,
+	or if it isn't a valid picture, <function>getimagesize</function>
+	will return <literal>NULL</literal> and generate a warning.
+   </para>
    <para>
     The optional <parameter>imageinfo</parameter> parameter allows
     you to extract some extended information from the image