diff --git a/fftools/ffmpeg_mux.h b/fftools/ffmpeg_mux.h
index f41f2c18fa..4ca8ab73a4 100644
--- a/fftools/ffmpeg_mux.h
+++ b/fftools/ffmpeg_mux.h
@@ -123,7 +123,7 @@ typedef struct Muxer {
 
 int mux_check_init(void *arg);
 
-static MuxStream *ms_from_ost(OutputStream *ost)
+static inline MuxStream *ms_from_ost(OutputStream *ost)
 {
     return (MuxStream*)ost;
 }