diff --git a/libavcodec/xsubdec.c b/libavcodec/xsubdec.c
index 4754987f54..9d3ba7f6ef 100644
--- a/libavcodec/xsubdec.c
+++ b/libavcodec/xsubdec.c
@@ -53,6 +53,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size,
     int w, h, x, y, rlelen, i;
     GetBitContext gb;
 
+    memset(sub, 0, sizeof(*sub));
     sub->format = 0;
 
     // check that at least header fits