diff --git a/libavcodec/libgsm.c b/libavcodec/libgsm.c
index 7623d35e815149969edd34a91ed3e4a3562913a7..16d9972f2c7251ccb6934af5dc95f0ad8973eea9 100644
--- a/libavcodec/libgsm.c
+++ b/libavcodec/libgsm.c
@@ -212,9 +212,12 @@ static int libgsm_decode_frame(AVCodecContext *avctx, void *data,
 
 static void libgsm_flush(AVCodecContext *avctx) {
     LibGSMDecodeContext *s = avctx->priv_data;
+    int one = 1;
 
     gsm_destroy(s->state);
     s->state = gsm_create();
+    if (avctx->codec_id == CODEC_ID_GSM_MS)
+        gsm_option(s->state, GSM_OPT_WAV49, &one);
 }
 
 AVCodec ff_libgsm_decoder = {