diff --git a/libavformat/isom.c b/libavformat/isom.c
index f0e7b8ef49..288049b779 100644
--- a/libavformat/isom.c
+++ b/libavformat/isom.c
@@ -159,6 +159,7 @@ const AVCodecTag codec_movaudio_tags[] = {
     { CODEC_ID_AMR_NB, MKTAG('s', 'a', 'm', 'r') }, /* AMR-NB 3gp */
     { CODEC_ID_AMR_WB, MKTAG('s', 'a', 'w', 'b') }, /* AMR-WB 3gp */
 
+    { CODEC_ID_GSM,  MKTAG('a', 'g', 's', 'm') },
     { CODEC_ID_ALAC, MKTAG('a', 'l', 'a', 'c') }, /* Apple Lossless */
     { CODEC_ID_QDM2, MKTAG('Q', 'D', 'M', '2') }, /* QDM2 */
 
diff --git a/libavformat/mov.c b/libavformat/mov.c
index f8d35a6dc9..a19e97093a 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -931,6 +931,7 @@ static int mov_read_stsd(MOVContext *c, ByteIOContext *pb, MOV_atom_t atom)
         st->codec->codec_type = CODEC_TYPE_AUDIO; /* force type after stsd for m1a hdlr */
         st->need_parsing = AVSTREAM_PARSE_FULL;
         break;
+    case CODEC_ID_GSM:
     case CODEC_ID_ADPCM_MS:
     case CODEC_ID_ADPCM_IMA_WAV:
         st->codec->block_align = sc->bytes_per_frame;