diff --git a/libavformat/subfile.c b/libavformat/subfile.c
index 2f9c7791c6..e6712806a9 100644
--- a/libavformat/subfile.c
+++ b/libavformat/subfile.c
@@ -18,6 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/avassert.h"
 #include "libavutil/avstring.h"
 #include "libavutil/opt.h"
 #include "avformat.h"
@@ -136,6 +137,8 @@ static int64_t subfile_seek(URLContext *h, int64_t pos, int whence)
     case SEEK_END:
         new_pos = end + pos;
         break;
+    default:
+        av_assert0(0);
     }
     if (new_pos < c->start)
         return AVERROR(EINVAL);