diff --git a/libmpcodecs/ad.h b/libmpcodecs/ad.h
index 9b1daf9e48..7127801b9d 100644
--- a/libmpcodecs/ad.h
+++ b/libmpcodecs/ad.h
@@ -22,6 +22,8 @@
 #include "mpc_info.h"
 #include "libmpdemux/stheader.h"
 
+extern float drc_level;
+
 typedef mp_codec_info_t ad_info_t;
 
 /* interface of video decoder drivers */