diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
index 872d62fc60892e90f45457839b6a7e8f5d43eed8..18452e984ddce699c765f539f99b48ad62740815 100644
--- a/libavfilter/avfilter.c
+++ b/libavfilter/avfilter.c
@@ -142,6 +142,7 @@ int avfilter_link(AVFilterContext *src, unsigned srcpad,
     link->cur_pic = NULL;
 
     /* find a format both filters support - TODO: auto-insert conversion filter */
+    link->format = -1;
     if(src->filter->outputs[srcpad].query_formats)
         fmts[0] = src->filter->outputs[srcpad].query_formats(link);
     else