diff --git a/libavfilter/formats.h b/libavfilter/formats.h
index 22224dce2d..d44890109e 100644
--- a/libavfilter/formats.h
+++ b/libavfilter/formats.h
@@ -198,6 +198,10 @@ void ff_channel_layouts_unref(AVFilterChannelLayouts **ref);
 void ff_channel_layouts_changeref(AVFilterChannelLayouts **oldref,
                                   AVFilterChannelLayouts **newref);
 
+/**
+ * Sets all remaining unset filter lists for all inputs/outputs to their
+ * corresponding `ff_all_*()` lists.
+ */
 av_warn_unused_result
 int ff_default_query_formats(AVFilterContext *ctx);