gif image in RTF

Hi,

I read on the FOP website, that gif images are supported in rtf output. I am 
using fop version 0.93.

With pdf and postscript everything is OK. But with rtf I get this error:

org.apache.fop.render.rtf.rtflib.rtfdoc.RtfExternalGraphic$ExternalGraphicException 
org.apache.fop.render.rtf.rtflib.rtfdoc.RtfExternalGraphic$ExternalGraphicException: 
The tag <fo:external-graphic> does not support gif - image type.

Does anyone know what to do? Are GIF images not supported???

Steffen